Open-source Slack alternatives

Rocket.Chat is a communications platform written in TypeScript for teams and organizations that care about data protection. It supports real-time conversations between colleagues, with partner companies, and with customers or citizens, and its topics place it in the same space as Slack, with WebRTC for calls and meetings.

The product emphasizes control over where and how it runs. Deployment options include self-hosted servers, a managed cloud and fully air-gapped environments, with a scalable architecture and performance monitoring for workspace administration. Security and sovereignty features, including identity management, are a core part of the pitch, and the platform is built to be highly customizable, so organizations can adapt it to their own workflows and integrations.

The repository's license is listed as 'Other' on GitHub, although the topics reference an MIT-licensed community core, so confirm which components fall under which terms before relying on it commercially. It suits government bodies, enterprises and regulated industries that want a Slack-style tool they can host themselves.

Mattermost is an open-core collaboration platform you host yourself, covering team chat, workflow automation, voice calls, screen sharing and AI integrations. This repository is the primary source for core development of the platform. The server is built with Go and React, ships as one Linux binary and depends on PostgreSQL. GitHub lists the license as 'Other'.

Each month, on the 16th, a newly compiled release is published under the MIT license. You can deploy Mattermost on-premises or try it in the cloud. The project highlights use cases such as DevSecOps, incident resolution and IT service desk, and it offers native clients for Android, iOS, Windows, macOS and Linux in addition to the web interface.

Installation options include Docker, Ubuntu, a tar archive, Kubernetes, Helm and an Omnibus package. Developers can build integrations through APIs, webhooks, slash commands, Apps and plugins, and the repository links product and developer documentation, security bulletins and contribution guides. It suits engineering, security and operations teams that want controlled, self-managed team messaging.

Zulip is an open-source team chat application whose defining feature is topic-based threading within channels. The idea is to blend the strengths of email and chat, so that remote and distributed teams can follow several conversations at once and catch up later without losing context. Its topics tag it as a Slack alternative.

The project is developed by a distributed community, with more than a thousand contributors and a steady flow of commits each month, and it says it has put effort into readable, tested code and extensive contributor documentation. The server is a Python web application, and there are web, desktop, built on Electron, and mobile clients, built with React Native. Zulip is used by companies and open-source projects alike, and the README says it is designed for both live and asynchronous communication.

Zulip is licensed under Apache-2.0. You can run the server on your own infrastructure, which gives full control over data, or use the hosted service operated by the project's company. It suits teams that find flat channel-based chat chaotic and want a more structured way to keep discussions organized.

Element Web is a client for Matrix, the open protocol for decentralized messaging. It is the web and desktop application formerly known as Vector and Riot, and it lets people join rooms, chat in teams and communities, and collaborate across Matrix servers rather than inside a single vendor's network.

The client is built with TypeScript on top of the Matrix JS SDK. The README defines support tiers for browsers, covering recent versions of Chrome, Firefox, Edge and Safari on desktop, best-effort handling for ESR and extended-stable releases, and community support for mobile web. For phones and tablets the maintainers recommend the native Element X apps for Android and iOS.

It is released under the AGPL-3.0 license and is typically served from your own web host or used through the hosted app from the vendor, Element. Related products such as Element Call and the Enterprise Server Suite are mentioned as part of the wider Element offering. Changes are tracked on GitHub with regular release cycles.

Campfire is a web-based group chat application that Basecamp offers as software you run yourself, with no subscription. It covers the features people expect from team chat, including multiple rooms with access controls, direct messages, @mentions and search.

Files can be attached to messages and previewed, notifications are delivered via Web Push, and an API supports bot integrations. The Docker image bundles the web app, background jobs, caching, file serving and SSL, so a single machine is enough for a complete deployment. A pre-built image is published on the GitHub container registry.

The simplest way to deploy is ONCE, a tool that walks through setup and keeps the instance up to date automatically; you can also run the Docker image directly by following the self-hosting guide. On first launch a wizard creates the admin account, whose email address appears on the sign-in page. Campfire is written in Ruby, licensed under MIT, and open to modification.

Synapse is a homeserver for the Matrix protocol, an open standard for decentralized, federated chat and real-time communication. It is written in Python using the Twisted framework, with performance-sensitive parts implemented in Rust, and is developed under the element-hq organization.

Running a homeserver lets a person or organization host their own accounts and chat rooms while still communicating with users on other Matrix servers. Synapse is licensed under AGPL-3.0, and its documentation is published at element-hq.github.io/synapse.

Macro is an all-in-one workspace for teams that brings messaging, mail, documents, tasks, AI agents, calls and customer records into a single quick interface. Everything in the workspace can be linked with @ mentions and searched, so people and agents do not have to hop between separate tools to find context.

The project grew from its founders' wish for a single operating system for their startup, after using Slack, Linear, Notion, HubSpot and Superhuman, which do not work together as one system. A shared team-level memory ties the pieces together. Repository topics reference Slack, Notion and Linear as comparison points, plus MCP and agent support. The code base is written in Rust and TypeScript.

Macro is licensed under AGPL-3.0 and offers a hosted sign-up, with documentation, a demo booking and a feature request channel linked in the README. It suits startups and small teams that want to replace a stack of separate collaboration tools.

Cinny is a client for the Matrix chat network that focuses on a simple, elegant and secure interface. The stated aim is an instant messaging application that is easy on people and has a modern look.

The web app is available at app.cinny.in and is updated on every release, while the dev branch is continuously deployed to a separate address that may be unstable. A desktop app is distributed from the cinny-desktop repository. The maintainers are currently replacing matrix-js-sdk with their own SDK and are not accepting pull requests until further notice.

To self-host Cinny, download the release tarball and serve the dist directory with any web server, or pull the Docker image from Docker Hub or the GitHub Container Registry. Default homeservers and explore pages are set in config.json, redirects need to be configured for assets, and hash routing is available as a fallback. Cinny is written in TypeScript and licensed under AGPL-3.0.

Element Android, also called Element Classic, is a previous-generation Matrix collaboration client for Android provided by Element. It runs on Android devices with Lollipop (API 21) or newer. The README says this client is still supported and receives security updates, but no new features or usability improvements are being made, and it recommends the next-generation Element X app instead. The code is written in Kotlin and licensed under AGPL-3.0.

The project is built on a new Android SDK written entirely in Kotlin, which shares the repository with the app during early development. At each release the SDK module is copied to the matrix-android-sdk2 repository so that third-party apps can use it as a regular Gradle dependency. The README also explains the delay between a GitHub release and its appearance on Google Play and F-Droid, which includes beta periods and store reviews.

This repository contains the services and libraries that power the Stoat chat service, whose earlier name Revolt still appears in the project's topics. It is a backend codebase written in Rust, using MongoDB for storage and Redis alongside it. The linked developer site documents the public API for people building on the platform.

The code is organized into core crates and server crates. The core crates cover configuration, the database implementation, file handling with S3 storage and encryption, API models, permission logic, user presence, shared result and error types, and a request coalescing service. On top of these sit a REST API server called delta and a WebSocket events server called bonfire.