Linphone - Linphone is an internet phone or Voice Over IP phone (VoIP).
Zoiper - Cross-platform VoIP softphone dialer for SIP and IAX systems
MicroSIP - MicroSIP is a free portable SIP softphone for Windows based on PJSIP stack.
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.
Phoner - Softphone for VoIP, CAPI und TAPI.
Sipnetic - Sipnetic is a free VoIP softphone based on the SIP protocol.