Linphone - Linphone is an internet phone or Voice Over IP phone (VoIP).
Communifire - Enterprise Social Collaboration Software
Zoiper - Cross-platform VoIP softphone dialer for SIP and IAX systems
DigitalChalk - Online Training Software and Learning Management System (LMS)
Sipdroid - Free and open-source SIP/VoIP Client
Workplace by Facebook - Connect everyone in your company and turn ideas into action.