Calls on Slack - Make voice calls in Slack
Skype for Slack - Move your slack discussions to a group skype call
OpenPhone - Simplest way to own a business phone number
Yodel - Group photo and video sharing. Create stories with friends, join stories from around the world.
Pingly - Your communication hub — Email, text & voice in one app
Houseparty - Brining empathy to online communication.