Open-source alternatives to Slack

MIT-licensed alternative to Slack and Mattermost with end-to-end encryption, Omnichannel, an apps marketplace, and FedRAMP-ready compliance.

Pricing: Free and self-hosted (MIT); paid Enterprise/Cloud tiers add omnichannel support and SLAs.

• Closest feature parity with Slack
• Large marketplace of apps and integrations
• Self-hosting requires more ops effort than Slack's SaaS
• Some enterprise features are gated behind a paid tier

MIT-licensed alternative to Slack with channels, threads, webhooks, Jira/GitHub integrations, and Playbooks for incident response. Desktop and mobile apps included.

Pricing: Free and self-hosted (MIT); paid Enterprise and Cloud tiers add SSO and compliance features.

• Strong DevOps integrations (Jira, GitHub, webhooks)
• Playbooks feature built for incident response
• UI feels less polished than Slack
• Some compliance features require the paid tier

Zulip is an open-source team chat application built around topic-based threading, which keeps conversations organized in a way that channel-only tools like Slack don't. Apache-2.0 licensed.

Pricing: Free and open source, self-hosted; also offers a hosted Zulip Cloud plan.

• Topic threading scales better for large, busy teams
• Fully open source, no paid-tier feature gating
• Topic-based model has a learning curve versus flat channels
• Smaller app/integration ecosystem than Slack

Element is an open-source, end-to-end encrypted collaboration client built on the decentralized Matrix protocol, so it can federate across independent servers rather than relying on one company's infrastructure.

Pricing: Free and self-hosted (AGPL-3.0); Element also sells hosted plans and enterprise support.

• Decentralized Matrix protocol avoids vendor lock-in
• End-to-end encryption by default
• Federation adds operational complexity
• Interface is less streamlined than centralized tools

Fluxer is a free, open-source instant messaging and VoIP platform for friends, groups, and communities, styled after Discord. AGPL-3.0 licensed with self-hosting support.

Pricing: Free and open source (AGPL-3.0), self-hosted.

• Discord-style UX familiar to many users
• Voice and video included
• Younger project, smaller community
• Fewer business-focused integrations than Slack

Campfire is a simple, self-hosted group chat application from 37signals, released as open source under the MIT license in 2025. It's deliberately minimal — @mentions, DMs, rooms — with no recurring subscription.

Pricing: One-time source-code purchase from 37signals, no subscription; self-hosted only.

• No recurring subscription cost
• Extremely simple, low operational overhead
• Minimal feature set — no threads, no video calls
• Not designed to scale to large organizations

Cinny is an open-source Matrix client focused on a simple, elegant interface for end-to-end encrypted conversations. AGPL-3.0 licensed, it connects to any Matrix homeserver.

Pricing: Free and open source (AGPL-3.0), self-hosted; requires a separate Matrix homeserver.

• Clean, focused interface
• Full Matrix end-to-end encryption
• Requires running or connecting to a Matrix homeserver separately
• Fewer built-in integrations than Slack

Stoat (formerly Revolt) is an open-source, self-hostable group chat platform styled after Discord — servers, channels, voice, and moderation — built in the EU with no ads or data mining.

Pricing: Free and open source (AGPL-3.0), self-hosted.

• Discord-style UX, EU-based with no ad tracking
• Active development
• Smaller community than established options
• Less mature for business or compliance use cases

Wire is an open-source, end-to-end encrypted collaboration platform for messaging, calls, and file sharing, aimed at organizations with strong security and compliance requirements. AGPL-3.0 licensed.

Pricing: Free and self-hosted (AGPL-3.0) via wire-server; Wire also sells hosted enterprise plans.

• Strong compliance and security track record, EU-based
• End-to-end encrypted calls and messaging
• Self-hosting wire-server is notably complex (many services)
• Smaller community than Rocket.Chat or Mattermost

Quiet is an open-source, peer-to-peer team chat that syncs messages directly between devices over Tor, with no central server, no phone number, and no metadata collection. GPL-3.0 licensed.

Pricing: Free and open source (GPL-3.0). No server to host.

• No server to host or maintain — fully peer-to-peer
• Maximum privacy: no phone number, no metadata
• No central history or backup if all devices are offline
• Not designed for large teams or enterprise use