RingCentral - RingCentral is the leading provider of cloud-based communications and collaboration solutions for small business and enterprise companies
Dialpad - Switch is a cloud-based phone system built for Google Apps users.
Twilio Video - Real-time video infrastructure and SDK
Truly Wireless - Wireless business phone system built for sales and support team.
CallHub - Predictive Call Center, Voice and Text Broadcasting app
Asterisk - An open source telephony switching and private branch exchange service for Linux.