Dialpad - Switch is a cloud-based phone system built for Google Apps users.
Linphone - Linphone is an internet phone or Voice Over IP phone (VoIP).
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.
Zoiper - Cross-platform VoIP softphone dialer for SIP and IAX systems
8x8 X Series - X Series connects teams across channels and around the globe, giving you access your most critical information securely, from any location.
Sipdroid - Free and open-source SIP/VoIP Client