ShoreTel - Cloud phone system & contact center software & services
FluffyChat - Open. Nonprofit. Cute ?
CorvisaOne - CorvisaOne is another cloud-based communications suite that is specially designed for companies that need features for managing inbound or outbound call centres.
TeleGuard - TeleGuard is a secure messenger that makes it store that your data or chats are not stored while collaborating or communicating with partners and friends.
8x8 X Series - X Series connects teams across channels and around the globe, giving you access your most critical information securely, from any location.
Molly (Signal fork) - Molly is an independent Signal fork for Android