Mumble - Mumble is an open source, low-latency, high quality voice chat software primarily intended for use...
Tox - Send messages, files, create groups and make Tox to Tox audio and video calls. Securely.
GSC - With GSC, you can pick from any of 14 worldwide datacenters to host your own free voice server.
qTox - A Qt graphical user interface for Tox.
TeamTalk - TeamTalk 4 is a conferencing system which enables a group of people to collaborate and share...
Signal - Fast, simple & secure messaging. Privacy that fits in your pocket.