Zoiper - Cross-platform VoIP softphone dialer for SIP and IAX systems
CallHippo - Easy to use Phone System with World-Class Support
MicroSIP - MicroSIP is a free portable SIP softphone for Windows based on PJSIP stack.
Callmama - Get cheap international calling, international virtual number, Call Mama Gives an added advantage to send message and make calls to non-user of Callmama App.
Sipnetic - Sipnetic is a free VoIP softphone based on the SIP protocol.
KrispCall - Virtual cloud phone system for business