qTox - A Qt graphical user interface for Tox.
Signal - Fast, simple & secure messaging. Privacy that fits in your pocket.
Tox - Send messages, files, create groups and make Tox to Tox audio and video calls. Securely.
BCM - Blockchain Messenger - BCM is a highly secure communication platform.
Toxic - Toxic is a client with an ncurses interface, written entirely in C.
FluffyChat - Open. Nonprofit. Cute ?