Tox - Send messages, files, create groups and make Tox to Tox audio and video calls. Securely.
RingCentral - RingCentral is the leading provider of cloud-based communications and collaboration solutions for small business and enterprise companies
qTox - A Qt graphical user interface for Tox.
Dialpad - Switch is a cloud-based phone system built for Google Apps users.
Signal - Fast, simple & secure messaging. Privacy that fits in your pocket.
Aircall - Aircall is a call center software of a new generation designed for fast growing companies. Setup instantly and integrates to your CRMs