Talk360 - Talk360 is a best-in-class communication utility that offers a convenient way to connect with loved ones globally.
Zoiper - Cross-platform VoIP softphone dialer for SIP and IAX systems
FluffyChat - Open. Nonprofit. Cute ?
MicroSIP - MicroSIP is a free portable SIP softphone for Windows based on PJSIP stack.
Textnow.com - It lets you text your friends, aka my only source of happiness
Sipnetic - Sipnetic is a free VoIP softphone based on the SIP protocol.