Daily.co for Intercom - Free video calls & screen shares embedded in Intercom
Clearbit for Slack - Send all signups directly to a Slack channel
Pluot Communications - Big-screen video conferencing for startups
Photostash - Automatically save your pictures from Slack to Gdrive
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.
Slack It - A bookmarklet to share links in Slack with one click