FluffyChat - Open. Nonprofit. Cute ?
ShoreTel - Cloud phone system & contact center software & services
Molly (Signal fork) - Molly is an independent Signal fork for Android
CorvisaOne - CorvisaOne is another cloud-based communications suite that is specially designed for companies that need features for managing inbound or outbound call centres.
Olvid - The most secure messaging app in the world.
8x8 X Series - X Series connects teams across channels and around the globe, giving you access your most critical information securely, from any location.