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.
Daily.co for Intercom - Free video calls & screen shares embedded in Intercom
Phonebot - Make phone calls from within a Slack channel
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.
Milligram - A minimalist CSS framework
CallKite - Your website’s video call center in just one click.