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Chat and messaging apps handle some of the most sensitive traffic on your devices, from work discussions to personal conversations, which makes it worth knowing exactly how the software works and where your messages actually go. Open source communication tools let you self-host your own server, audit the encryption, or simply avoid a platform that mines conversations for advertising data.

Signal and Session focus on private, encrypted personal messaging. Element is a Matrix client built for decentralized, federated chat. Mattermost, Rocket.Chat, and Zulip are self-hostable team chat platforms aimed at replacing tools like Slack or Microsoft Teams for organizations that want to keep their data in-house.

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Popular Open Source Communication Apps

Element

Secure, decentralized messaging app

Element is a free, open source messaging app built on the Matrix protocol, offering end-to-end encryption, decentralized hosting, and team collaboration.

Open Source AGPL-3.0

Mattermost

Self-hosted team messaging for developers and enterprises

Mattermost is a self-hosted, open source team messaging platform built for developers and enterprises, offering an MIT-licensed core with an optional paid Enterprise Edition.

Open Source Team Edition: MIT · Enterprise Edition: proprietary commercial license

Rocket.Chat

Open source team chat with an omnichannel customer service layer

Rocket.Chat is a self-hosted, open source team chat and customer service platform, offering an MIT-licensed Community Edition alongside a paid Enterprise Edition with omnichannel support.

Open Source Community Edition: MIT · Enterprise Edition: proprietary commercial license

Session

Decentralized messenger with no phone number required

Session is a free, open source messenger that requires no phone number or email, routing encrypted messages through a decentralized onion-routing network instead of central servers.

Open Source GPL-3.0

Signal

Open source, end-to-end encrypted messenger

Signal is a free, open source messaging app with end-to-end encryption enabled by default for all chats, calls, and groups, run by a non-profit foundation instead of a for-profit company.

Open Source AGPL-3.0

Zulip

Open source team chat organized by topic threads

Zulip is a free, fully open source team chat app under the Apache-2.0 license, built around topic-threaded conversations designed to keep asynchronous discussions organized and easy to catch up on.

Open Source Apache-2.0