Team chat

Open-source alternatives to Slack

2 self-hostable options you can run on your own server, compared on facts from GitHub (fetched Oct 21, 2026).

Side-by-side comparison

Tool	Rocket.Chat	Mattermost
GitHub stars	46,305	39,400
License	Custom / see repo	Custom / see repo
Last push	Oct 21, 2026 Active	Oct 21, 2026 Active
Forks	14,019	9,061
Open issues + PRs	4,205	1,083
Main language	TypeScript	TypeScript
Links	Repo · Website	Repo · Website

Highlighted cells mark the highest star count and the most recent push. Source: GitHub REST API, per-tool links on each tool page. Copyleft licenses (AGPL/GPL) require sharing modifications if you distribute or (AGPL) serve them; check the repo license before deploying.

The options

Rocket.Chat

Team chat

The Secure CommsOS™ for mission-critical operations

46k Custom / see repo Active

Replaces Slack

Mattermost

Team chat

Mattermost is an open source platform for secure collaboration across the entire software development lifecycle..

39k Custom / see repo Active

Replaces Slack