Houseparty - Brining empathy to online communication.
Mumble - Mumble is an open source, low-latency, high quality voice chat software primarily intended for use...
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!
RaidCall - Free & Light. Setting up is fast and easy; with no need to rent or set up servers. Low CPU usage and minimum memory footprint allows for smooth, uninterrupted communication. im. Group Communication.