Re: Cave Johnson here...
Nice! I'd wager they're all the same engine under the hood, with varying degrees of front ends bolted on at the last minute by teams of donut eating developers just trying to make it through the quarter without being bothered.
Here's my Teams issue, other than the obligatory "not another chat system for work!":
Linux devops, contractor, could have a Mac, but will use the Dell to save my employer a few bucks and just run my junk in a nice CentOS VM. So, we have Outlook installed on my Win7 Dell, check. We have Skype, check. We have Slack, check. We just got Teams, check. And now we're looking at O365 migration, and now Teams is on there, check. Out of all that, only Slack seems like a sane solution to watch what's going on. The rest of this is wildly unnecessary for most needs, and no one uses the video chatting on anything unless you prop up an astonishingly expensive video chat system from Cisco, or those other guys, in the conference room. No one who is even slightly sane video chats from their desk. Even teens don't bother to FaceTime each other, they just snapchap and text.
Teams, the desktop app is HIGHLY UNSTABLE and would constantly update itself throughout the day, even when I shut it off. It was uninstalled because of this. So, I guess I'll hang out in the Teams O365 to see if the other two people in my group who are two cubes away from me will "chat me up" on this new service no one asked for. Why bother when there are too many solutions to a problem that email already fixed in the 1980s. FFS! And I do NOT mean Female, Female, Shark!
Innovation: "Hey look, I reinvented the wheel and added sparkles and GIFs and O365 Team integration!"