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
Talko for Slack - Team calls for mobile & web in any Slack channel
Yodel - Group photo and video sharing. Create stories with friends, join stories from around the world.
Freshcaller - Freshcaller is a modern-day reimagining of our everyday phone system for customer support, sales, IT, and HR teams.