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.
GSC - With GSC, you can pick from any of 14 worldwide datacenters to host your own free voice server.
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.
Toxic - Toxic is a client with an ncurses interface, written entirely in C.