WhatsApp - WhatsApp Messenger: More than 1 billion people in over 180 countries use WhatsApp to stay in touch with friends and family, anytime and anywhere.
Bulma - Bulma is an open source CSS framework based on Flexbox and built with Sass. It's 100% responsive, fully modular, and available for free.
Quickie - 3-60 second video calls with your friends
Phonebot - Make phone calls from within a Slack channel
Messenger Video Calls - Facebook Messenger, now with HD video calls
Milligram - A minimalist CSS framework