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Best Open-Source Slack Alternatives (2026)

27 self-hostable, open-source projects that replace Slack — without per-seat pricing and a capped message history. Each is scored for how hard it is to self-host, with one-click deploy options where they exist.

Slack charges per seat and, on the free plan, hides messages past a history cap so your own conversations become inaccessible until you pay. Self-hosting removes both: unlimited members, unlimited searchable history, and chat data that stays on your servers.

Our picks at a glance

Easiest to self-host
The Lounge

Difficulty 2/5; a self-hosted web IRC client that is by far the lightest option, though it is IRC rather than a full Slack clone.

Most powerful
Rocket.Chat

The most feature-complete communications platform here, with channels, voice/video, integrations and broad deployment options.

Most active
Rocket.Chat

At ~45k stars it leads this list in momentum.

Best managed option
Rocket.Chat

Managed:yes with an official cloud offering, so you can adopt it without running the server yourself.

Compare all 27 alternatives

ProjectDeployManagedLicense
Rocket.Chat
TypeScript
46k ★
3/5
Moderate
One-Click
Docker
+3
MIT2 days agoRepo
Novu
Docker
39k ★
3/5
Moderate
Docker
Docker Compose
MIT2 days agoRepo
Mattermost
Go
38k ★
3/5
Moderate
One-Click
Docker
+3
MIT2 days agoRepo
ntfy
Go
31k ★
2/5
Easy
Docker
Docker Compose
+1
Apache-2.03 days agoRepo
Huly
TypeScript
26k ★
4/5
Involved
Docker
Docker Compose
+2
EPL-2.02 days agoRepo
Zulip
Python
25k ★
3/5
Moderate
Docker Compose
Manual
Apache-2.02 days agoRepo
Apprise
Python
17k ★
2/5
Easy
Docker
Docker Compose
+1
MIT4 days agoRepo
Gotify
Go
15k ★
2/5
Easy
Docker
Docker Compose
+1
MIT4 days agoRepo
Tinode
Go
13k ★
3/5
Moderate
Docker
Docker Compose
+1
GPL-3.04 days agoRepo
Element (Web)
TypeScript
13k ★
4/5
Involved
Docker
Manual
AGPL-3.02 days agoRepo
SimpleX Chat
Haskell
11k ★
4/5
Involved
Docker
Manual
AGPL-3.02 days agoRepo
Screego
Docker
10k ★
2/5
Easy
Docker
Docker Compose
+1
GPL-3.01 month agoRepo
Centrifugo
Go
10k ★
3/5
Moderate
Docker
Docker Compose
+2
MIT4 days agoRepo
Typebot
Docker
10k ★
3/5
Moderate
Docker
Docker Compose
AGPL-3.03 days agoRepo
Mumble
C++
8.1k ★
3/5
Moderate
Docker
Manual
BSD-3-Clause11 days agoRepo
The Lounge
TypeScript
6.3k ★
2/5
Easy
Docker
Manual
MIT2 days agoRepo
WorkAdventure
Docker
5.5k ★
4/5
Involved
Docker
Docker Compose
AGPL-3.02 days agoRepo
Synapse (Matrix Homeserver)
Python
4.3k ★
4/5
Involved
Docker
Docker Compose
+2
AGPL-3.02 days agoRepo
Weechat
C
3.3k ★
4/5
Involved
Manual
GPL-3.03 days agoRepo
Ergo
Go
3.2k ★
3/5
Moderate
Docker
Manual
MIT9 days agoRepo
One Time Secret
Docker
2.8k ★
2/5
Easy
Docker
Manual
MIT3 days agoRepo
Tox
C
2.6k ★
4/5
Involved
Manual
GPL-3.04 days agoRepo
WBO
Nodejs
2.6k ★
2/5
Easy
Docker
Manual
AGPL-3.02 days agoRepo
Stoat
Rust
2.5k ★
3/5
Moderate
Docker
Docker Compose
+1
AGPL-3.01 month agoRepo
AnyCable
Go
2.3k ★
4/5
Involved
Docker
Docker Compose
+1
MIT5 days agoRepo
Chitchatter
Nodejs
2.3k ★
1/5
Effortless
One-Click
Manual
GPL-2.02 days agoRepo
Nextcloud Talk
JavaScript
2.1k ★
3/5
Moderate
Docker
Docker Compose
+1
AGPL-3.02 days agoRepo

What to look for: Match the threading model to how your team actually communicates, since Zulip's topic-based model and channel-based tools like Mattermost feel very different day to day. Also check integrations, mobile and desktop clients, and whether you want federation (Matrix) or a single self-contained server.

Head-to-head:Rocket.Chat vs SlackNovu vs SlackMattermost vs Slackntfy vs SlackHuly vs Slack

The alternatives, reviewed

  1. #1
    Rocket.Chat
    Self-host: Moderate

    Fully customizable open-source communications platform and Slack alternative

    46k TypeScript MIT 2 days ago
    How it compares to Slack
    • Resource-heavy (Node.js + MongoDB) and can be slow at scale on modest hardware
    • Some enterprise features (engagement dashboard, scalability, advanced auth) require a paid plan
    • UI can feel cluttered compared to Slack
    • Mobile apps have historically lagged the web client in polish
    RepoDetails & deploy →
  2. #2
    Novu
    Self-host: Moderate

    Open-source notification infrastructure for multi-channel developer alerts

    39k Docker MIT 2 days ago
    How it compares to Slack
    • Not a real-time team chat; it is a notification delivery layer, not a conversation platform.
    • Self-hosted setup requires Postgres, MongoDB, Redis, and S3-compatible storage, adding operational burden.
    • Managed cloud features (advanced analytics, SLA guarantees) are not available in the open-source edition.
    • Mobile SDK for in-app notifications has fewer features than commercial equivalents like OneSignal.
    RepoDetails & deploy →
  3. #3
    Mattermost
    Self-host: Moderate

    Open-source, self-hostable Slack alternative for secure team messaging and collaboration

    38k Go MIT 2 days ago
    How it compares to Slack
    • Many advanced features (LDAP/AD, SAML/SSO, compliance exports, high availability) are gated behind paid Enterprise tiers
    • Search and message UX feel less polished than Slack
    • Voice/video calling is more limited than Teams' full meetings stack
    • Smaller third-party app/integration marketplace than Slack
    RepoDetails & deploy →
  4. #4
    ntfy
    Self-host: Easy

    Simple HTTP-based push notifications to phone and desktop, no account needed

    31k Go Apache-2.0 3 days ago
    How it compares to Slack
    • No team chat, threading, or message history browsing; designed for one-way push alerts only.
    • No rich message formatting, file sharing, or reactions.
    • Rate limiting and attachment storage on the free public server are intentionally restrictive.
    • iOS push requires routing through ntfy's own APNs proxy unless you self-compile the app.
    RepoDetails & deploy →
  5. #5
    Huly
    Self-host: Involved

    All-in-one project management, tracker, and team collaboration - a Linear/Jira alternative

    26k TypeScript EPL-2.0 2 days ago
    How it compares to Slack
    • Self-hosting the full multi-service architecture (MongoDB, MinIO, Elastic, transactors) is complex
    • Documentation for self-hosting is sparse relative to its breadth
    • Breadth over depth: individual modules are less mature than dedicated tools like Linear or Slack
    • Self-hosted edition trails the managed cloud on some features
    RepoDetails & deploy →
  6. #6
    Zulip
    Self-host: Moderate

    Open-source team chat with a unique topic-based threading model

    25k Python Apache-2.0 2 days ago
    How it compares to Slack
    • Native voice/video calling is limited and usually relies on third-party integrations (Jitsi, Zoom)
    • The topic-threading model has a learning curve and can feel unfamiliar to Slack users
    • Production installs effectively want a dedicated server; multi-host scaling is involved
    • Smaller app/integration ecosystem than Slack
    RepoDetails & deploy →
  7. #7
    Apprise
    Self-host: Easy

    Python library and CLI to send notifications to 70+ services via one unified API

    17k Python MIT 4 days ago
    How it compares to Slack
    • Not a chat platform; Apprise only dispatches notifications, it has no UI for reading or replying to messages.
    • The optional apprise-api REST service is minimal and not production-hardened with auth by default.
    • No scheduling, retry queuing, or delivery tracking beyond what the target service provides.
    • Configuration is URL-string based, which can be verbose and error-prone for complex setups.
    RepoDetails & deploy →
  8. #8
    Gotify
    Self-host: Easy

    Self-hosted push notification server with Android app and REST API

    15k Go MIT 4 days ago
    How it compares to Slack
    • Android-only official mobile client; no native iOS app.
    • No team or group channels, threading, or conversation history beyond a simple message list.
    • No file attachments, rich formatting, or reactions.
    • Development has slowed; the project receives infrequent updates compared to alternatives like ntfy.
    RepoDetails & deploy →
  9. #9
    Tinode
    Self-host: Moderate

    Open-source instant messaging server with a Go backend and multi-platform clients

    13k Go GPL-3.0 4 days ago
    How it compares to Slack
    • More of a messaging backend/SDK than a turnkey Slack workspace experience
    • Lacks built-in app marketplace, workflows, and rich integrations of Slack
    • Voice/video is limited compared to Teams
    • Admin and team-management UI is minimal
    RepoDetails & deploy →
  10. #10
    Element (Web)
    Self-host: Involved

    Matrix-based secure messenger and Slack alternative with end-to-end encryption

    13k TypeScript AGPL-3.0 2 days ago
    How it compares to Slack
    • Requires running and maintaining a separate Matrix homeserver (e.g. Synapse) for a full deployment
    • End-to-end encryption key management and device verification can confuse non-technical users
    • Performance and load times lag native Slack/Teams clients in large rooms
    • Threads and search are less refined than Slack
    RepoDetails & deploy →
  11. #11
    SimpleX Chat
    Self-host: Involved

    The most private chat platform — no user IDs, double ratchet E2E encryption

    11k Haskell AGPL-3.0 2 days ago
    How it compares to Slack
    • No web client; primarily mobile-focused with a desktop CLI and early-stage desktop app.
    • Self-hosting the SMP server requires manual Haskell build or Docker and knowledge of relay configuration.
    • No workspace/org structure, channels, or administrative tooling suitable for business teams.
    • Integrations and bots ecosystem is minimal compared to Slack or Discord.
    RepoDetails & deploy →
  12. #12
    Screego
    Self-host: Easy

    Browser-based screen sharing for one or many viewers using WebRTC

    10k Docker GPL-3.0 1 month ago
    How it compares to Slack
    • Screen sharing only; no video/audio conferencing, chat, or file transfer features.
    • No persistent rooms, user accounts, or scheduling; sessions are ephemeral.
    • No recording capability.
    • TURN server must be open to the internet for external users, requiring firewall configuration.
    RepoDetails & deploy →
  13. #13
    Centrifugo
    Self-host: Moderate

    Language-agnostic real-time messaging server over WebSocket and SSE

    10k Go MIT 4 days ago
    How it compares to Slack
    • Developer-facing infrastructure component, not an end-user chat application; requires custom UI.
    • Managed hosting (Centrifugal Cloud) is still early and not yet a full Pusher replacement in pricing.
    • Persistent message storage requires an external database; Centrifugo only provides a short-term history buffer.
    • No built-in admin UI for channel management or user monitoring beyond basic metrics.
    RepoDetails & deploy →
  14. #14
    Typebot
    Self-host: Moderate

    Drag-and-drop conversational form builder embeddable in any website or app

    10k Docker AGPL-3.0 3 days ago
    How it compares to Slack
    • Focused on conversational forms/chatbots, not team messaging; does not replace Slack for internal communication.
    • Self-hosted version lacks some cloud-only integrations and the AI block that requires an OpenAI key.
    • No native payment processing; requires Stripe integration setup separately.
    • Result export and advanced analytics are more limited than Typeform's paid tiers.
    RepoDetails & deploy →
  15. #15
    Mumble
    Self-host: Moderate

    Low-latency, high-quality open-source voice and text chat for gaming and teams

    8.1k C++ BSD-3-Clause 11 days ago
    How it compares to Slack
    • Desktop client only; no official mobile apps with full feature parity (third-party clients exist but are limited).
    • No text channel persistence, message history search, or file sharing beyond basic in-channel text.
    • UI is dated and less polished compared to Discord or Teams.
    • No video calling, screen sharing, or integrations with productivity tools.
    RepoDetails & deploy →
  16. #16
    The Lounge
    Self-host: Easy

    Modern, self-hosted web IRC client for always-on team chat

    6.3k TypeScript MIT 2 days ago
    How it compares to Slack
    • It is an IRC client, so you still need IRC servers/networks for actual chat
    • IRC lacks native threads, rich file sharing, and message editing that Slack offers
    • No built-in voice/video or app integrations
    • Persistence and history depend on a connected bouncer/IRC setup
    RepoDetails & deploy →
  17. #17
    WorkAdventure
    Self-host: Involved

    Virtual office and conference as an interactive 16-bit RPG world in the browser

    5.5k Docker AGPL-3.0 2 days ago
    How it compares to Slack
    • Self-hosting requires managing 6+ Docker services (pusher, back, front, map-storage, Jitsi, etc.) with non-trivial coordination.
    • Not a general-purpose team chat tool; lacks threaded messaging, async communication, and integrations found in Slack.
    • Video quality and reliability depend on the separately self-hosted Jitsi instance.
    • Map creation requires proficiency with the Tiled map editor; onboarding is steep for non-technical teams.
    RepoDetails & deploy →
  18. #18
    Synapse (Matrix Homeserver)
    Self-host: Involved

    Reference Matrix homeserver powering decentralized, federated team chat

    4.3k Python AGPL-3.0 2 days ago
    How it compares to Slack
    • It is a backend only; you must pair it with a client (Element) for a usable product
    • Federation and database (PostgreSQL) tuning is required for scale and can be resource-intensive
    • Setup involves reverse proxy, TLS, well-known config, and federation ports
    • AGPL license and commercial relicensing have caused community friction
    RepoDetails & deploy →
  19. #19
    Weechat
    Self-host: Involved

    Fast, extensible terminal IRC and chat client with a rich plugin ecosystem

    3.3k C GPL-3.0 3 days ago
    How it compares to Slack
    • Terminal-only; no native graphical UI, making onboarding difficult for non-technical users.
    • Third-party plugins are required for any non-IRC protocol, and plugin quality and maintenance vary.
    • No file sharing, image preview, video calls, or rich message formatting out of the box.
    • Configuration is fully text-based with a steep learning curve for advanced setups.
    RepoDetails & deploy →
  20. #20
    Ergo
    Self-host: Moderate

    Modern IRCv3 server in Go combining ircd, services framework, and bouncer

    3.2k Go MIT 9 days ago
    How it compares to Slack
    • IRC protocol only; no voice, video, reactions, or rich embeds expected by modern chat users.
    • No web client included; users need a separate IRC client (WeeChat, HexChat, etc.) or an IRC-to-web bridge.
    • Message history is limited and not searchable at scale compared to Slack's enterprise search.
    • No integrations with productivity tools (calendars, task managers, CI/CD) without external bridges.
    RepoDetails & deploy →
  21. #21
    One Time Secret
    Self-host: Easy

    Share sensitive data via self-destructing links viewable only once

    2.8k Docker MIT 3 days ago
    How it compares to Slack
    • No real-time team chat; purpose-built only for one-shot secret sharing, not general messaging
    • No user accounts or team management UI out of the box
    • Lacks audit logs, access controls, or an admin dashboard found in enterprise chat platforms
    • No integrations with CI/CD or ticketing systems without custom development
    RepoDetails & deploy →
  22. #22
    Tox
    Self-host: Involved

    Distributed, serverless messenger with encrypted audio and video calls

    2.6k C GPL-3.0 4 days ago
    How it compares to Slack
    • No web or mobile app; all official clients are desktop-only with varying levels of polish
    • No persistent message history server-side; messages are lost if the recipient is offline at delivery time
    • No team workspaces, channels, or role-based permissions
    • Bootstrap node setup and NAT traversal can be unreliable behind strict firewalls
    RepoDetails & deploy →
  23. #23
    WBO
    Self-host: Easy

    Real-time collaborative whiteboard for drawings, diagrams, and notes

    2.6k Nodejs AGPL-3.0 2 days ago
    How it compares to Slack
    • No authentication or access control; any board URL is publicly accessible by default
    • No user management, versioning, or export to common vector formats (SVG/PDF)
    • No sticky-note templates, voting, or structured retrospective tooling
    • Boards stored as flat JSON files; no database means limited scalability for large teams
    RepoDetails & deploy →
  24. #24
    Stoat
    Self-host: Moderate

    User-first self-hosted team chat platform built with Rust

    2.5k Rust AGPL-3.0 1 month ago
    How it compares to Slack
    • Relatively new project; ecosystem of integrations and bots is minimal compared to Slack
    • No voice or video calling built in
    • Mobile apps not yet as mature as established competitors
    • Plugin/app marketplace does not exist yet
    RepoDetails & deploy →
  25. #25
    AnyCable
    Self-host: Involved

    High-performance realtime server for WebSockets and Server-Sent Events

    2.3k Go MIT 5 days ago
    How it compares to Slack
    • It is a realtime transport layer, not a full chat product; requires significant custom development to build a user-facing app
    • gRPC configuration and tuning adds operational complexity
    • No built-in UI, user management, or message persistence — all delegated to the application layer
    • Managed AnyCable Cloud only available for certain plans
    RepoDetails & deploy →
  26. #26
    Chitchatter
    Self-host: Effortless

    Serverless peer-to-peer ephemeral chat with no accounts required

    2.3k Nodejs GPL-2.0 2 days ago
    How it compares to Slack
    • No message history; all chats are ephemeral and disappear on page close
    • No file sharing, threads, reactions, or integrations
    • WebRTC NAT traversal can fail on restrictive corporate networks
    • No moderation, authentication, or access control features
    RepoDetails & deploy →
  27. #27
    Nextcloud Talk
    Self-host: Moderate

    Self-hosted chat, video calls, and conferencing integrated into Nextcloud

    2.1k JavaScript AGPL-3.0 2 days ago
    How it compares to Slack
    • Requires a running Nextcloud installation as a prerequisite
    • Larger group video calls need a separate High Performance Backend (Janus/signaling server) to scale
    • Chat features are less rich than dedicated platforms like Slack
    • Fewer third-party app integrations focused on messaging
    RepoDetails & deploy →

The verdict

Rocket.Chat is the best overall Slack replacement on features, momentum and managed hosting; choose Mattermost if you prefer a Go-based, ops-friendly server, or Zulip if your team would benefit from its topic-threaded model.

Still deciding? Compare Rocket.Chat vs Novu side by side →

Slack alternatives — frequently asked questions

What is the best open-source alternative to Slack?

Rocket.Chat and Mattermost are the two leading channel-based Slack alternatives, both MIT-licensed and self-hostable. Rocket.Chat is the most feature-rich, while Mattermost is a clean Go server many teams prefer for operations.

Which Slack alternative is easiest to self-host?

The Lounge is the lightest at difficulty 2/5, but it is a web IRC client rather than a Slack clone. Among full Slack-style platforms, Rocket.Chat, Mattermost and Zulip are all difficulty 3/5 and offer One-Click or Docker deployment.

Is there a free self-hosted Slack alternative with unlimited history?

Yes. Self-hosting Rocket.Chat (MIT), Mattermost (MIT) or Zulip (Apache-2.0) gives you unlimited, fully searchable message history with no per-seat cost, which directly fixes Slack's history cap and pricing.

Which alternative supports end-to-end encryption?

Element (Web) on the Matrix protocol provides end-to-end encrypted messaging, backed by a Synapse homeserver. This is the strongest privacy option here and also gives you federation across servers.

What if I want threaded conversations instead of channels?

Zulip is built around a topic-based threading model that keeps parallel discussions organized, which is its main differentiator. It is Apache-2.0, self-hostable at difficulty 3/5, and also offers managed hosting.

Can I get managed hosting instead of running the server myself?

Rocket.Chat, Mattermost, Zulip, Element and Synapse all offer managed hosting (managed:yes). Tinode and The Lounge are self-host-only.

Keep exploring

All Team Chat & Collaboration →Self-hosted directory →Easiest to self-host →
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