Linphone - Linphone is an internet phone or Voice Over IP phone (VoIP).
Tragofone - White-label VoIP Softphone with WebRTC and Auto-provisioning
MicroSIP - MicroSIP is a free portable SIP softphone for Windows based on PJSIP stack.
Jami - Application and Data, Collaboration, and Web and Video Conferencing
We-Talk - Free online chat rooms where people chat and meet each other and chat with the stranger and learn new cultures and make friends.
PhonerLite - PhonerLite enables your PC to use it for internet telephony (VoIP , Voice over IP, SIP).