CallHippo - Easy to use Phone System with World-Class Support
Zoiper - Cross-platform VoIP softphone dialer for SIP and IAX systems
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.
MicroSIP - MicroSIP is a free portable SIP softphone for Windows based on PJSIP stack.
KrispCall - Virtual cloud phone system for business
Sipnetic - Sipnetic is a free VoIP softphone based on the SIP protocol.