Slack

Team chat priced per seat, with history limits on free plans and everything on Salesforce's servers.

5 self-hosted replacements in this index, ranked by GitHub stars in the dataset.

Replacements

Discourse
Advanced forum / community solution based on Ruby and JS.
48,046 stars Active
2 Nov 2026 _gh-attach-assets
Rocket.Chat
Communications platform that puts data protection first.
46,357 stars Active
31 Oct 2026 9.0.0-rc.3
Mattermost
Platform for secure collaboration across the entire software development lifecycle, can be integrated with Gitlab.
39,499 stars Active
2 Nov 2026 v11.7.15-rc1
Zulip
Powerful group chat application.
26,154 stars Active
1 Nov 2026 13.0-rc1
Element
Fully-featured Matrix client for Web, iOS & Android.
13,633 stars Active
30 Oct 2026 v1.12.33