Misakey - Send encrypted documents & messages to anyone
Mumble - Mumble is an open source, low-latency, high quality voice chat software primarily intended for use...
Wire - Private & Secure Messenger
GSC - With GSC, you can pick from any of 14 worldwide datacenters to host your own free voice server.
WhatsApp - WhatsApp Messenger: More than 1 billion people in over 180 countries use WhatsApp to stay in touch with friends and family, anytime and anywhere.
Discord - Step up your game with a modern voice & text chat app. Crystal clear voice, multiple server and channel support, mobile apps, and more.