Synapse

Realtime server for reliable two-way communication over WebSockets, Server-sent events, etc

Notification server for relaying push notifications via Matrix, similar to PushBullet and Gotify

E-book library manager that can view, convert, and catalog e-books in most of the major e-book...

Secured and decentralized communication system. Offers decentralized chat, forums, messaging, file...

Whistleblowing software enabling anyone to easily set up and maintain a secure reporting platform

Zulip is a powerful, open source group chat application