Tragofone - White-label VoIP Softphone with WebRTC and Auto-provisioning
Zoho Meeting - Free video conferencing, online meeting, desktop sharing solution from Zoho.
PhonerLite - PhonerLite enables your PC to use it for internet telephony (VoIP , Voice over IP, SIP).
Airtime - Hang out with group video, share music & videos
tSIP - tomeko.net/software: SIP client for Windows.
Voxox CloudPhone - Get a local or toll-free business number that automatically answers, routes and transfers calls, plus other professional business phone services.