Best Open Source Slack Alternatives

Open-source chat solution offering real-time messaging, video calls, and file sharing for teams of all sizes.

Mattermost provides a flexible, open-source platform for secure team collaboration, designed for organizations with strict security and privacy requirements.

Nextcloud offers on-premises file sync, sharing and collaboration platform with advanced security and privacy features.

An open-source platform that combines project management, team communication, document collaboration, and virtual office spaces in one integrated solution.

Zulip is an open-source team chat app that uses threaded conversations to keep communication organized and efficient for teams of all sizes.

Open-source platform for encrypted communication, file sharing, and collaboration based on the Matrix protocol.

Free, open-source instant messaging and VoIP platform with full Markdown support, voice/video calls, moderation tools, and self-hosting options for communities.

Open-source collaboration platform combining real-time chat, document editing, file sharing, and project management. Self-host for complete control.

Install your own group chat system with @mentions, DMs, and mobile support. One-time purchase, no monthly fees. Includes full source code for customization.

Cinny offers a simple, elegant, and secure interface for Matrix-based conversations, protected by end-to-end encryption.

Modern chat platform featuring text channels, community building tools, fine-grained permissions, and complete privacy protection. Open-source and ad-free.

A comprehensive collaboration platform offering end-to-end encrypted messaging, file sharing, and video calls with enterprise-grade security and compliance features.

Build your own community space for gaming, chatting, and hanging out with friends worldwide. Customize your environment for the perfect social experience.

Open-source communication platform with multi-window chat, economy systems, and privacy-first approach. Built by communities for superior performance.

Open source chat server with end-to-end encryption, clustering support, and comprehensive messaging features for building real-time communication apps

Free Matrix-based messenger with end-to-end encryption, multi-platform bridges, and on-premise deployment. Connect across 30+ networks securely.