Important: Telegram's clients are open source, its server is not
Telegram publishes the source of its apps, but not its server, and regular chats are encrypted between you and Telegram rather than end to end. The alternatives here fill different gaps: Signal for private one-to-one and group messaging with a fully open-source server, Matrix clients such as Cinny and Twake Chat for federation, Stoat for community servers, and Quiet for serverless operation.
Closest to Telegram
Signal is closest for everyday messaging, with groups, media, and calls, but it requires a phone number and lacks Telegram's public channels and bots. Stoat is closest for large communities with channels, roles, and moderation. Matrix clients offer federated rooms and bridges to other networks.
Federation and self-hosting
Cinny and Twake Chat are Matrix clients that connect to any Matrix homeserver, so you can run your own server and federate with other Matrix users. Twake Chat also offers bridges to more than 30 networks. Stoat can be self-hosted as your own community chat server. Signal is a centralized service, and Quiet is peer-to-peer.
License details
Signal's apps and server, Cinny, Stoat, and Twake Chat are AGPL-3.0, and Quiet is GPL-3.0. Signal's service is run by the Signal Foundation and is free to use.
Maintenance status
Signal, Cinny, Stoat, Quiet, and Twake Chat were all updated within days or weeks of this update. Twake Chat is a young project with a small community.