Open Source Messaging App
Encryption of message content has become common, so the real differentiator in a private messenger is the metadata - who talks to whom, how often, and from where - which a central server still sees even when it cannot read a word. The same label also covers two unrelated jobs: a personal messenger built around a threat model, and a team platform meant to replace workplace chat. Open source matters here because you can read the encryption yourself instead of trusting a claim, choose an architecture that keeps your social graph off any server, and run the whole thing on infrastructure you control rather than a vendor's account system.
Rocket.Chat
Open source team communications platform with messaging, voice, video, federation, and apps
Mattermost
Open source self-hosted collaboration platform with chat, workflow automation, voice, and screen sharing
Jitsi Meet
Open source video conferencing for browsers, mobile apps, self-hosted servers, and embedded meetings
Element
Matrix web and desktop client for end-to-end encrypted messaging and decentralized collaboration
SimpleX Chat
Private messenger with no user IDs, link or QR based connections, and double ratchet end to end encryption
Quiet
Encrypted p2p team chat with no servers, built on Tor and IPFS
Spacebar
Self-hosted Discord backend reimplementation with backward compatibility for existing bots, apps, and clients
Delta Chat
Decentralized desktop messenger with multi-profile, multi-device chat and chatmail relay support
Wire
End-to-end encrypted messenger for organizations, with a web client and server-side deployment
Our picks
These split across two jobs and several trust models, so match the pick to what you are actually replacing.
Self-hosted team communications platform: Rocket.Chat A full platform for internal and external communication, bundling messaging, voice, video, and federation with role and attribute-based access control. It runs self-hosted, in the cloud, or air-gapped, and a marketplace plus Apps-Engine connect it to existing systems.
Federated messaging on the open Matrix network: Element A Matrix client for teams that want interoperability instead of a walled garden, so people on different homeservers and other Matrix apps can talk. Messages are end-to-end encrypted, and you can point it at your own homeserver or a hosted service.
Private messenger with no user identifiers: SimpleX Chat Built to communicate without any user identifier, not even a random one. You connect by sharing a link or QR code, its relay servers keep no user records, and double ratchet encryption protects both content and metadata.
Offline-first messaging for high-risk situations: Briar Made for activists and journalists who need to talk when infrastructure is hostile or gone. It syncs device to device over Tor when online and over Bluetooth or Wi-Fi when the internet is down, with no account or phone number, and publishes reproducible builds you can verify.
Sorting private messengers from team platforms
Who controls identity - a domain, a phone number, an email address, or a key on your device - shapes everything downstream, so settle that question before comparing features. The label itself hides two unrelated products. Personal messengers like Session, Briar, and SimpleX Chat drop accounts and central servers to keep the social graph off anyone's infrastructure, while team platforms like Rocket.Chat and Mattermost are built around channels, roles, integrations, and administration for an organization. A couple of entries are neither: playSMS manages SMS gateways and bulk texting, and Jitsi Meet is video conferencing rather than persistent chat.
Network architecture is the next fork. A single-server platform is easiest to operate and moderate but usually reaches outside your organization only through guest accounts or bridges. Federation, as Element uses over Matrix, gives each group its own domain and policy while making abuse handling and version drift real concerns. Peer-to-peer designs such as Briar and Quiet remove the server entirely and can sync over Bluetooth or Tor, at the cost of harder multi-device sync and push notifications. Delta Chat takes a different route again, riding ordinary email so anyone with an address can be reached.
Treat encryption as a trade-off rather than a checkbox. End-to-end encryption protects content from the server but complicates search, history recovery on a new device, and bots that would otherwise read every message. For self-hosting, mobile push delivery is the detail that surprises teams most, so test notification speed and battery impact on real phones before moving a whole group. And confirm what metadata the design still leaves visible, because that is usually the thing a private messenger is really trying to hide.
Related categories
Frequently asked questions
Is a private messenger the same thing as a team chat platform?+
No, and mixing them up is the usual reason a rollout stalls. Personal messengers like Session, SimpleX Chat, and Briar are built around a threat model, dropping accounts and central servers to protect who talks to whom. Team platforms like Rocket.Chat and Mattermost are built around channels, roles, integrations, and administration for an organization. Decide which job you are solving before you compare anything else.
What can a messaging server still learn if messages are encrypted?+
Even with unreadable content, a central server can usually see the metadata: which accounts talk, how often, message sizes, timing, and the IP addresses connecting. That social graph is often more revealing than the words. Designs that fight this remove identifiers or route around the server, as SimpleX Chat does with no user IDs and Session does by sending traffic through an onion network.
Can I message people without handing over a phone number or email?+
Yes, several here are built for exactly that. Session needs no phone number or email and routes over the Oxen node network. SimpleX Chat uses no user identifiers at all; you connect by sharing a link or scanning a QR code. Briar has no central account either, keeping contacts and history only on the devices that hold them.
Do any of these work when the internet is down?+
Briar is designed for it, syncing directly between nearby devices over Bluetooth or Wi-Fi when there is no connection and switching to Tor when the internet returns. Quiet also syncs peer to peer between team devices without a central server. That resilience is the reason these tools appeal to activists and journalists working in disrupted or hostile conditions.
How does end-to-end encryption change search and message history?+
When the server cannot read messages, it usually cannot index them either, so full-text search happens on each device after local decryption and can be slower or incomplete on a fresh install. History on a new device depends on a verified device or an encrypted key backup, not a server copy. If your team needs global search or retention, confirm those workflows before adopting an encrypted-by-default tool.
Do self-hosted messaging apps deliver mobile push notifications reliably?+
This is the detail to test first, not last. Mobile operating systems impose background limits and often expect a push gateway, so notification speed, call alerts, and battery impact vary by app and deployment. Server-backed platforms like Mattermost and Rocket.Chat have mature mobile clients, while peer-to-peer designs handle background delivery differently. Verify arrival speed on real Android and iOS phones before committing a group.
Which of these can replace Slack or Discord for a team?+
For a Slack-style platform, Rocket.Chat and Mattermost both offer channels, threads, voice, integrations, and administration, self-hosted. Quiet is a smaller, server-less alternative that syncs over Tor for groups that want no central server at all. If you specifically need Discord compatibility, Spacebar reimplements the Discord backend so many existing bots and clients can connect to a server you run.
What is federation, and when do I actually want it?+
Federation lets separate servers interoperate, so users on different domains can talk without one central owner. Element uses this over the Matrix network, which is useful when you want to reach people outside your organization or avoid a single vendor. The cost is operational: abuse handling, discovery, and version drift become network-wide governance rather than a local setting, so weigh that against a simpler single server.