replacing Slack
Open Source Slack Alternatives
Channel-based team messaging platform — Slack pricing: $8.75-$12.50/user/month. Below: 4 free,
self-hostable open source projects that cover the same ground, ranked by real GitHub adoption.
There are 4 open source Slack alternatives tracked on this registry, against Slack pricing of $8.75-$12.50/user/month. The most-adopted is Mattermost with 39,093 GitHub stars, written in TypeScript. Together the set has 108,406 stars across 2 languages and 2 licences. All 4 are free to self-host with no licence fee, and 4 of 4 received a commit in the last 90 days. 4 head-to-head Slack comparisons are available.
Slack's free plan retains only 90 days of message history — for a team that communicates daily, that is a rolling memory loss. Enterprise Grid pricing requires annual contracts and custom quotes. Every message, file, and integration lives on Slack's servers.
Our top 3 Slack alternatives
Mattermost is an open core, self-hosted collaboration platform. It bundles chat, workflow automation, voice calling, screen sharing, and AI integration into one system. This repository is the primary source for core development on the platform. The codebase is written in Go and React, organised as a monorepo, and the server runs as a single Linux binary that relies on PostgreSQL. A new compiled version is released under an MIT license every month on the 16th. Native clients exist for Android, iOS, Windows PC, macOS, and Linux, alongside the web interface, with the React Native client code living in the same monorepo.
NOASSERTION · TypeScript · Slack vs Mattermost →
Jitsi Meet is an open-source video conferencing platform built on WebRTC standards, designed for privacy-focused, account-free video calls. It operates as a standalone web application or embeddable component, supporting both browser-based and native mobile usage without requiring user accounts to join meetings. The project lives in the video-communication ecosystem, competing directly with proprietary services like Zoom, Google Meet, and Slack’s built-in calling.
Apache-2.0 · TypeScript · Slack vs Jitsi →
Zulip is a team chat server and web application written in Python and released under the Apache-2.0 licence. Its defining idea is topic-based threading, which the project describes as combining the best of email and chat: every conversation inside a channel gets its own named topic rather than being appended to one undifferentiated stream. The server ships alongside native clients for desktop through Electron and for mobile through React Native, and the whole product is developed by a distributed community of contributors rather than a single vendor.
Apache-2.0 · Python · Slack vs Zulip →
last updated nightly · ranking method: github stars, live-tracked
Frequently asked questions
What is the best open source alternative to Slack?
Mattermost is the most-starred open source alternative to Slack in this registry, with 39,093 GitHub stars. 4 alternatives are compared here in total.
Are there free alternatives to Slack?
Yes. Every project listed on this page is open source and free to self-host — there is no licence fee. Some projects also sell a managed hosted version, but the self-hosted path costs nothing.
What should I look at when replacing Slack?
Compare licence terms, community size (stars), primary language and release activity. A fast-moving project with a compatible licence and an active maintainer base matters more than raw star count when you are committing to a migration.