RingCentral - RingCentral is the leading provider of cloud-based communications and collaboration solutions for small business and enterprise companies
tSIP - tomeko.net/software: SIP client for Windows.
Aircall - Aircall is a call center software of a new generation designed for fast growing companies. Setup instantly and integrates to your CRMs
PhonerLite - PhonerLite enables your PC to use it for internet telephony (VoIP , Voice over IP, SIP).
Nextiva - Business VoIP, cloud phone systems trusted by more than 150,000 companies. Powered by the leading cloud PBX VoIP platform, Nextiva is rated the best business VoIP service provider.
Jami - Application and Data, Collaboration, and Web and Video Conferencing