Mumble is an open-source, low-latency, high quality voice chat software.
Mumble is an Open Source, low-latency and high-quality voice-chat program written on top of Qt and Opus.
The Secure CommsOS™ for mission-critical operations
Mattermost is an open source platform for secure collaboration across the entire software development lifecycle..
Jitsi Meet - Secure, Simple and Scalable Video Conferences that you use as a standalone app or embed in your web application.
Zulip server and web application. Open-source team chat that helps teams stay productive and focused.
A glossy Matrix collaboration client for the web.
Synapse: Matrix homeserver written in Python/Twisted + Rust