Linphone - Linphone is an internet phone or Voice Over IP phone (VoIP).
Dialpad - Switch is a cloud-based phone system built for Google Apps users.
Zoiper - Cross-platform VoIP softphone dialer for SIP and IAX systems
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.
Sipdroid - Free and open-source SIP/VoIP Client
Genesys Cloud - As the foundation of great customer experience, the Genesys PureCloud contact center platform empowers your business to provide excellent service across the entire customer journey.