Voxer - Turn your phone into a Walkie Talkie. Don't waste time on phone calls and voicemails.

Chatib - Chatib is an online chat room where you can meet and chat with new people, make them friends, or even data them online.

NextPlane - NextPlane offers cloud-based, scalable unified communications federation service for the enterprise.

Element.io - Secure messaging app with strong end-to-end encryption, advanced group chat privacy settings, secure video calls for teams, encrypted communication using Matrix open network. Riot.im is now Element.

Sameroom - Chat interoperability-as-a-service

Kandan - Open Source private chat server. Your own private Chat server in minutes, plus additional features.