Skype for Slack - Move your slack discussions to a group skype call
Zoom - Equip your team with tools designed to collaborate, connect, and engage with teammates and customers, no matter where you’re located, all in one platform.
Calls on Slack - Make voice calls in Slack
Face to Face - Video meetups for online communities (PH room password meow)
Pingly - Your communication hub — Email, text & voice in one app
HandsFree 2 - Call and SMS in Mac using your Android phone via Bluetooth