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

qTox - A Qt graphical user interface for Tox.

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

Tox - Send messages, files, create groups and make Tox to Tox audio and video calls. Securely.

Vivox - Vivox is called to be one of the leading chatting platforms for online gamers.

Signal - Fast, simple & secure messaging. Privacy that fits in your pocket.