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

Voxer - Turn your phone into a Walkie Talkie. Don't waste time on phone calls and voicemails.

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

Sameroom - Chat interoperability-as-a-service

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.

Chromacam - Chromacam is a tool that offers virtual green screen for web conferencing and presentations.