Tightens the 'slack' in Slack :-) . Slack but with all the things that you wish slack also did [properly]. Namely realtime media such as voice and video. Integrates with video conferencing hardware as well as digital white boarding. Nice user experiences beyond just messaging. The online meeting capability is 2nd to none in my opinion.
A single client that delivers Enterprise Messaging, Meeting and Calling capabilities
Can be difficult to keep with all the new features!