13 Best Open Source Alternatives to Slack

Updated July 2026

Slack rarely loses teams on the quality of its chat; it loses them on everything wrapped around it: message history that disappears behind the free plan's limit, per-seat pricing that climbs with every hire, and years of conversation sitting in a vendor's cloud on retention terms you don't set. The open source alternatives below move that history onto infrastructure you control, so search, files, and audit logs live in your own database rather than someone else's. The trade is real, since you take on hosting, upgrades, and mobile push notifications, but in return the conversations, the integrations, and the compliance controls become yours to keep, extend, and export on your own schedule.

1.Rocket.Chat

45.5kOtherTypeScript Self-host

Rocket.Chat is an open source communications platform for team messaging, including conversations with external stakeholders such as customers or citizens. It suits organizations that need secure, customizable communication across real-time and asynchronous conversations, and this card covers the self-hosted open source edition.

Real-time messaging for internal and external communication
Voice calls, video, and federation
Identity management with end-to-end encryption
Role and attribute-based access control

More about Rocket.Chat Visit website

2.Mattermost

37.8kOtherTypeScript Self-host

Mattermost is an open core, self-hosted collaboration platform for secure team communication across the software development lifecycle. This card describes the open source self-hosted server; a hosted cloud option also exists for teams that want to try it without running their own instance.

Chat, workflow automation, voice calling, and screen sharing
AI integration for collaboration workflows
APIs, webhooks, slash commands, apps, and plugins
Clients for web, Android, iOS, Windows, macOS, and Linux

More about Mattermost Visit website

3.Huly

26.2kEPL-2.0TypeScript Self-host

Huly is an open-source all-in-one app for teams that bundles project management, chat, CRM, HRM, and applicant tracking into one workspace. It is built as a replacement for Linear, Jira, Slack, and Notion, giving teams one place for issues, communication, customer records, HR workflows, and hiring.

Project management for issues and tasks
Built-in team chat
CRM for customer records
HRM and applicant tracking for hiring workflows

More about Huly Visit website

4.Zulip

25.4kApache-2.0Python Self-host

Zulip is an open source team chat app for distributed teams of all sizes. Its topic-based threading combines email-style organization with chat, so conversations stay focused and easy to follow across both live and asynchronous work.

Topic-based threading with streams and topics
Designed for both live and asynchronous conversations
Self-host on Ubuntu or Debian Linux
Docker deployment option

More about Zulip Visit website

5.Element

13.2kAGPL-3.0TypeScript Self-host

Element is a Matrix web and desktop client for secure messaging and collaboration. It connects people on the open Matrix network and can be self-hosted or used through Element Matrix Services, giving organizations a choice of where their data lives.

Matrix-based web client for messaging and collaboration
End-to-end encrypted messenger
Runs as a desktop app in Electron
Self-hosted deployment or Element Matrix Services

More about Element Visit website

6.SimpleX Chat

11.2kAGPL-3.0Haskell

SimpleX Chat is a private and encrypted messenger for people who want to communicate without user identifiers of any kind, not even random ones. It protects messages and metadata, including who you talk to and when, and lets you make a private connection before any messaging starts.

No user identifiers; connect by link or QR code
Protects messages and metadata
Double ratchet end to end encryption with an extra layer
Android and iOS mobile apps

More about SimpleX Chat Visit website

7.Quiet

2.6kGPL-3.0C

Quiet is a private team chat app for groups that do not want a central server. It is an alternative to Slack, Discord, and Element, and it syncs data directly between team devices over Tor with no server required.

Direct device-to-device sync over Tor
Communities with owner-issued invitation codes
Channels, images, and large file sharing
Desktop notifications and keyboard controls

More about Quiet Visit website

8.Twake

1.9kAGPL-3.0TypeScript Self-host

Twake is a secure open source collaboration platform built to improve how organizations work together. It brings team chat, file storage, a shared team calendar, task management, video calls, and real-time document collaboration into a single digital workplace.

Team chat for everyday communication
File storage for shared documents
Shared team calendar and task management
Video calls and conferencing

More about Twake Visit website

9.Delta Chat

1.5kGPL-3.0TypeScript Self-host

Delta Chat is a decentralized, secure messenger that delivers chats over the email network. Instead of a proprietary server, it can sign up to interoperable chatmail relays, so your messages travel like email but stay end-to-end encrypted.

Decentralized chat that travels over the email network
End-to-end encrypted messaging without a phone number
Multiple profiles and multiple devices
Chat-shared tools and small games inside conversations

More about Delta Chat Visit website

10.Wire

1.2kGPL-3.0TypeScript Self-host

Wire is a secure messenger built for organizations and trusted by millions of people worldwide. It is designed around end-to-end encryption, so message content stays protected and collaboration happens without compromising on privacy.

End-to-end encrypted messaging for organizations
Browser-based web client for team collaboration
Open source client you can build and run yourself
Self-hosted deployment via packaged server or Docker

More about Wire Visit website

11.Session

774GPL-3.0Kotlin

Session is a private messenger for Android that aims to remove any chance of metadata collection. It routes all messages through an onion routing network that obfuscates users' IP addresses, so you can talk without handing over a phone number, an email, or the connection details that usually trail a conversation.

Onion routing that obfuscates users' IP addresses
No metadata collection of message routing
Decentralized Oxen Service Node network, no central server
Service Nodes store messages offline for later delivery

More about Session Visit website

12.Briar

636OtherJava

Briar is a messaging app for activists, journalists, and anyone who needs a safe way to communicate. It does not rely on a central server, so messages sync directly between users' devices instead of through a hosted service.

Direct device-to-device message sync without a central server
Sync over Bluetooth or Wi-Fi when the Internet is unavailable
Sync over Tor to resist surveillance when online
Messages and contacts stored only on your own devices

More about Briar Visit website

13.Jami

259OtherShell

Jami is a distributed, open source communication platform. Rather than routing conversations through a central service, it is built as a distributed system, which keeps communication in the hands of the people using it.

Distributed communication platform with no central service
Daemon plus client architecture shared across platforms
GNOME desktop client that runs its own daemon
Runs on Linux, macOS, and Android

More about Jami Visit website

Our picks

The right choice depends on how close to Slack you want to stay.

Closest all-around replacement: Rocket.Chat Rocket.Chat covers the most Slack ground in a single platform: real-time messaging, voice calls, video, and federation, plus end-to-end encryption and role- and attribute-based access control. Public apps install from its Marketplace and you can build custom ones with the Apps-Engine, so integrations stay extensible. It self-hosts with Docker, Podman, or Kubernetes, or runs air-gapped.

Best for technical teams: Mattermost Mattermost is built around the software development lifecycle, pairing chat with workflow automation, voice calling, and screen sharing. It runs as a single Go binary over PostgreSQL, which keeps self-hosting simple, and its MIT-licensed core plus 700+ integrations, webhooks, and slash commands make rebuilding Slack automations straightforward.

Best for asynchronous teams: Zulip Zulip's defining feature is topic-based threading: messages live in channels and then in named topics, so people follow exactly the conversations they care about instead of scrolling a firehose. That model suits distributed teams mixing live and async work. It self-hosts on Ubuntu, Debian, or Docker and is licensed under Apache 2.0.

No-server, peer-to-peer option: Quiet For groups that want no central server, Quiet syncs messages, files, and channels directly between members' devices over Tor, with end-to-end encryption and owner-issued invitation codes. It is GPL-licensed and still early software missing some features of mature chat apps, so weigh it as a privacy-first choice rather than a like-for-like swap.

What actually changes when you leave Slack

How much of Slack you are actually replacing decides everything that follows. If you want a near-drop-in messenger, Rocket.Chat and Mattermost stay closest to the channels, threads, and DMs model your team already knows, and both add voice, video, and integrations. If leaving is a chance to rethink the format, Zulip's topic-based threading is a genuine change that many distributed teams prefer. If chat is really tangled up with project work, Huly folds messaging into issues, CRM, and hiring in one workspace. And if you refuse any central server at all, Quiet syncs directly between devices.

The features to test are the ones Slack makes invisible: mobile push notifications, search ranking, link previews, calls, and outside collaboration. Rocket.Chat and Mattermost cover the most ground here, Rocket.Chat with voice, video, federation, end-to-end encryption, and access control, Mattermost with voice calling, screen sharing, and 700+ integrations. Enterprise needs like SSO, retention, and audit trails usually exist but take design work, so map them against your real org chart before committing rather than assuming one-to-one parity with Slack's admin controls.

Migration begins with a Slack export, not a live clone. Public channel history moves most cleanly; private channels, DMs, threads, reactions, and files depend on your plan and export approval, and often arrive as an archive to search rather than live conversation. Treat integrations as a separate project: incoming webhooks are easy to recreate, but Slack apps, slash commands, and workflow steps use Slack-specific APIs and need rebuilding. Configure identity and SSO first, run both systems briefly, then freeze Slack and archive the old workspace once search and alerts check out.

Related alternatives

Discord15 TeamViewer8 Spotify24 Plex5 PubNub8 Zoom3

Frequently asked questions

Can I bring Slack's threads and searchable history with me?+

Partly. A Slack workspace export gives you message data, but completeness depends on your plan, retention settings, and approval for private content. Public channel messages move most reliably; threads, reactions, mentions, and attached files may not map exactly. The realistic plan is to import history as a searchable archive first, then decide which conversations actually need to become live again in the new tool.

Which alternative feels most like Slack day to day?+

Rocket.Chat and Mattermost stay closest to the Slack experience of channels, threads, direct messages, and app integrations, so the daily muscle memory carries over. Zulip deliberately differs: its conversations are organized into named topics inside channels, which reads differently at first but suits teams drowning in busy channels. If you want the smallest adjustment, start with one of the first two.

Do these support voice, video, and huddle-style calls?+

Yes, though depth varies. Rocket.Chat includes voice calls and video alongside messaging and federation. Mattermost provides voice calling and screen sharing built into channels. These cover most day-to-day needs, but test audio reliability, mobile behavior, and screen sharing under your real network conditions before retiring Slack calls, since quick ad hoc huddles are a common gap area for chat platforms.

Will our Slack apps, slash commands, and webhooks keep working?+

Not directly. Incoming webhooks and simple alerts are usually easy to recreate, but Slack apps, slash commands, and workflow steps rely on Slack-specific APIs and have to be rebuilt. Mattermost helps here with 700+ marketplace integrations, webhooks, slash commands, and plugins, and Rocket.Chat has its Apps-Engine and Marketplace. Inventory each integration by owner and impact, then rebuild the critical ones before cutover.

How is Zulip's topic-based threading different from Slack channels?+

In Slack, a busy channel is one long stream you scroll and thread selectively. Zulip groups every message into a named topic within a channel, so you can read or mute one conversation at a time and catch up on exactly the threads you care about. It is especially useful for distributed teams mixing live and asynchronous work, though it takes a short adjustment.

Can we message people outside our company, like Slack Connect?+

This needs planning, because external access is often woven into sales, support, and vendor workflows. Rocket.Chat is explicitly built for conversations with external stakeholders such as customers, and supports federation across organizations. Element can also federate across servers through Matrix, while most other tools rely on guest accounts or separate workspaces instead. Decide early who can invite outsiders, what they can see, and how you revoke access when a project ends.

Is there a Slack alternative that needs no server at all?+

Quiet is exactly that: it syncs messages, files, and channels directly between members' devices over Tor, with no central server to run, and access is granted through owner-issued invitation codes. Everything is end-to-end encrypted between members. It is still early software that lacks some features of mature chat apps, so treat it as a privacy-first option rather than a full Slack replacement.