Video SDK from Zoom - Build fully customizable video-based apps
RingCentral - RingCentral is the leading provider of cloud-based communications and collaboration solutions for small business and enterprise companies
Amazon Chime - Online meetings and video conferencing
Truly Wireless - Wireless business phone system built for sales and support team.
AuthKey.io - SMS API and WhatsApp Business API
Asterisk - An open source telephony switching and private branch exchange service for Linux.