Linphone is one of the most famous open source softphones in the world. It is fully SIP-based, for all calling, presence and IM features.
MicroSIP is a free portable SIP softphone for Windows based on PJSIP stack. It allowing to do high quality VoIP calls (P2P or on regular telephones) via open SIP protocol. From cloud of SIP providers you can choose best for you, register account and use it with MicroSIP. You'.
Zoiper IAX & SIP multilanguage and multiplatform (Windows, Linux and Mac OS X) softphone is a VoIP soft client, meant to work with any IP-based communications systems and infrastructure.
PhonerLite enables your PC to use it for internet telephony (VoIP , Voice over IP, SIP). You need an internet connection and an account from a provider supporting the SIP protocol.
Telephone allows you to make phone calls over the Internet or your company network. If your phone line supports SIP protocol, you can use it on your Mac instead of a physical phone anywhere you have a decent network connection.
WebCall offers free high-quality audio and video telephony based on WebRTC 1.0. All data is delivered from peer to peer. The P2P links are always end-to-end encrypted. WebCall provides web applications for caller and callee.
With a superbly designed and intuitive user interface, the softphone offers easy set up with lots of preconfigured VoIP providers built in and smart call management features. Enjoy high quality enterprise communication features with zero effect on battery life.
Silent Phone – Secure Encrypted Video & Voice Mobile Phone Calls
You now have the ability to have secure encrypted phone calls between Silent Circle members, anywhere, anytime, with complete control.
Make a secure call as easy as an ordinary call and be sure of real safety.