MicroSIP - MicroSIP is a free portable SIP softphone for Windows based on PJSIP stack.
Communifire - Enterprise Social Collaboration Software
Linphone - Linphone is an internet phone or Voice Over IP phone (VoIP).
DigitalChalk - Online Training Software and Learning Management System (LMS)
Zoiper - Cross-platform VoIP softphone dialer for SIP and IAX systems
Workplace by Facebook - Connect everyone in your company and turn ideas into action.