Mumble - Mumble is an open source, low-latency, high quality voice chat software primarily intended for use...

Houseparty - Brining empathy to online communication.

GSC - With GSC, you can pick from any of 14 worldwide datacenters to host your own free voice server.

Booyah - Video chat with up to 12 friends at the same time.

Discord - Step up your game with a modern voice & text chat app. Crystal clear voice, multiple server and channel support, mobile apps, and more.

Slack - A messaging app for teams who see through the Earth!