XO Hosted PBX - Hosted PBX is a scalable UC solution that uses cloud technology to integrate HD voice & data services, mobility, along with advanced calling
CloudTalk - Work locally, grow globally
Zoiper - Cross-platform VoIP softphone dialer for SIP and IAX systems
Webinato - Webinato is a platform for webinar automation.
Sipdroid - Free and open-source SIP/VoIP Client
VoIP.ms - VoIP.ms is a VoIP origination and termination tool.