tSIP - tomeko.net/software: SIP client for Windows.
Tragofone - White-label VoIP Softphone with WebRTC and Auto-provisioning
PBXware - PBXware is the world’s first and most mature IP PBX Professional Open Standards Turnkey Telephony Platform. Bicom Systems’ softswitch is offered in the Business, Call Center and Multi-Tenant Editions each supporting specific features.
YakYak - Desktop client for Google Hangouts
CommPeak PBX - CommPeak’s Hosted Cloud IP-PBX is a web-based highly customizable and feature-rich solution - the ideal, low-cost solution for an enterprise of all sizes.
Lingo - Empower Creation and Ensure Brand Consistency. Build and Share libraries of visual assets with your entire team — all from your desktop.