13 Best Open Source Alternatives to Slack

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

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

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

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

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

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

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

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

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

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

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

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

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