The best alternative to Slack is Rocket.Chat, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 100 alternatives to Slack and 12 are so hopefully you can find a suitable replacement. Other interesting alternatives to Slack are AirSend, Quiet Chat, Buzz and Fleep.
Open-source chat server supporting real-time group, direct, and private messaging, video calls, file sharing, helpdesk chat, API integrations, desktop notifications, emojis, LDAP authentication, cross-platform apps, and customizable extensions for teams.
AirSend is a simple collaboration space for professionals and small teams that brings all your conversations, files, notes, and to-do lists into one place so that you can get work done faster and easier.
Peer-to-peer group chatting over Tor and IPFS, with local-first encrypted messaging and no central servers, offers privacy-focused decentralized collaboration for teams, supporting desktop and mobile. FOSS, open to contributors, and avoids surveillance-based tracking.
Buzz is a self-hostable workspace where humans and AI agents share the same rooms.
Fleep is a messenger for your teams and projects. It enables communication within and across organizations - be it your team chats, project communication or 1:1 conversations.
Blink is a team and employee app, with a Feed, Chat and Hub (for documents, links, files). Blink enabled you to organise your teams communication and content in one place. The Feed is both an internal social feed and integrates with external apps.
Campfire is an installable, self-hosted group chat system. Easily invite people. Make rooms. @mentions, DMs, and mobile support. The basics done right. And since you get the code and host it yourself, you can customize it however you’d like for your own use.
Communication without limits. The modern chat platform with servers, channels, direct messages and passwordless magic login.
GitChat is a free, open-source IDE extension that brings real-time developer chat, GitHub-based social networking, and repo community channels into VS Code, Cursor, and compatible editors - without leaving your coding environment.
Redesigned team chat with built-in Deep Work Mode, notification batching, focus status, and transparent public-first channels. Includes AI thread summaries for fast catch-up, thread inbox, real-time messaging with threads, and mobile apps. Setup in minutes.
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Does everything Slack does AND it's open source. However, it's also self-hosted. This means you have to put in the effort to set it up, but you control your own data, which is a huge advantage to your privacy - your chats and files don't sit on someone else's servers, ready for them or hackers to look at.