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6 self-hosted options

Open-source alternatives to Slack

The best open-source alternative to Slack is Rocket.Chat (MIT, 46,329 GitHub stars, Docker image). Mattermost stands out for a published Docker image, and Zulip stands out for the most commits in the last 12 months (5,095).

About Slack: A team messaging platform with channels, threads and integrations.

Updated · data from GitHub, refreshed daily

Top picks

  1. Rank 1:

    Rocket.Chat

    RocketChat/Rocket.Chat

    Communications platform that puts data protection first (alternative to Gitter.im and Slack).

    Active · last commit Oct 26, 2026

    Team ChatTypeScriptDocker

    Stands out for the most GitHub stars.

  2. Rank 2:

    Mattermost

    mattermost/mattermost

    Platform for secure collaboration across the entire software development lifecycle, can be integrated with Gitlab (alternative to Slack).

    Active · last commit Oct 26, 2026

    Team ChatTypeScriptDocker

    Stands out for a published Docker image.

  3. Rank 3:

    Zulip

    zulip/zulip

    Zulip is a powerful, open source group chat application.

    Active · last commit Oct 26, 2026

    Team ChatPython

    Stands out for the most commits in the last 12 months (5,095).

At a glance

Slack alternatives compared

Open-source apps come first, then source-available ones and apps whose license appsgit could not verify; within each group, projects with at least 12 commits in the last 12 months come before less active or archived ones, then by GitHub stars.

Slack alternatives compared, data as of 2026-10-26
AppStands out forLicenseGitHub starsCommits (12 mo)Last commitDocker image
Rocket.Chatthe most GitHub starsMIT46,3292,441Oct 26, 2026Yes
Mattermosta published Docker imageAGPL-3.039,4342,159Oct 26, 2026Yes
Zulipthe most commits in the last 12 months (5,095)Apache-2.026,1145,095Oct 26, 2026No
Element–AGPL-3.013,6143,188Oct 23, 2026No
Synapsethe most recent release (v1.163.2, October 2026)AGPL-3.04,735933Oct 24, 2026No
Stoat–AGPL-3.02,67733Oct 7, 2026Yes

Full list

All 6 Slack alternatives

Open any app for live stats, license details and a deploy option.

  1. 1

    Rocket.Chat

    Communications platform that puts data protection first (alternative to Gitter.im and Slack).

    Stands out for the most GitHub stars. Rocket.Chat has 46,329 GitHub stars, uses the MIT license, ships a Docker image and had 2,441 commits in the last year.

  2. 2

    Mattermost

    Platform for secure collaboration across the entire software development lifecycle, can be integrated with Gitlab (alternative to Slack).

    Stands out for a published Docker image. Mattermost has 39,434 GitHub stars, uses the AGPL-3.0 license, ships a Docker image and had 2,159 commits in the last year.

  3. 3

    Zulip

    Zulip is a powerful, open source group chat application.

    Stands out for the most commits in the last 12 months (5,095). Zulip has 26,114 GitHub stars, uses the Apache-2.0 license and had 5,095 commits in the last year.

  4. 4

    Element

    Fully-featured Matrix client for Web, iOS & Android.

    Element has 13,614 GitHub stars, uses the AGPL-3.0 license and had 3,188 commits in the last year.

  5. 5

    Synapse

    Server for Matrix, an open standard for decentralized persistent communication.

    Stands out for the most recent release (v1.163.2, October 2026). Synapse has 4,735 GitHub stars, uses the AGPL-3.0 license and had 933 commits in the last year.

  6. 6

    Stoat

    Stoat is a user-first chat platform built with modern web technologies.

    Stoat has 2,677 GitHub stars, uses the AGPL-3.0 license, ships a Docker image and had 33 commits in the last year.

FAQ

Slack alternatives: FAQ

Still curious? Email info@appsgit.com.

Is there a free alternative to Slack?

Yes. All 6 apps on this page are open source and free to self-host, so you can replace Slack without per-user fees. You pay only for the server.

Can I self-host an alternative to Slack with Docker?

Yes. 3 of the 6 apps here publish a Docker image, including Rocket.Chat, Mattermost and Stoat, so you can run them on a home server or VPS with Docker Compose.

Which Slack alternative is the most actively developed?

Zulip (Apache-2.0), with 5,095 commits in the last 12 months. Activity is a good sign that bugs and security issues get fixed.

How is this list ranked?

Open-source apps come first, then source-available ones and apps whose license appsgit could not verify; within each group, projects with at least 12 commits in the last 12 months come before less active or archived ones, then by GitHub stars.