It'd be hard to argue that MS has a monopoly on real time collaboration software when Slack exists.

It'd be similarly difficult to argue they're acting anti-competitively when Slack is thriving.

I think usually the argument is that they're leveraging an _existing_ foothold to gain advantage in a _new_ market. So the existing foothold is MS Office and MS Office 360, and the new market is messaging.

How they gained this foothold in desktop productivity software is left as an exercise to the reader.

Hey, thanks! I don't know much about antitrust, so this is likely to be a dumb question;

Why is messaging a new/different market for Microsoft regarding O365? Microsoft has been including business-targeted messaging/collab tools in O365 for years. Skype for Business preceded Slack, let alone Office Communicator or Linc, not to mention Outlook.

Is using existing products to leverage yourself into a new market anticompetitive, or "how any company expands into a new market?"

Depends on the scale of your foothold

> Slack is thriving.

Is Slack profitable?

$780m profit in 2021.

Are you really suggesting to break up a company simply based solely on your dissatisfaction with the product?

the bundled packaging where they give it away for free to get market share is a well documented antitrust practice.

Lookup diapers.com for instance. Amazon sold diapers below cost to gain marketshare, took all customers from diapers.com, those guys went bankrupt, and Amazon upped the prices to higher levels than before.

I am not suggesting breaking up Microsoft and Teams, I am suggesting that giving away Teams for free should not be allowed, it needs to be fairly priced. But Microsoft has good lawyers of course.

Do calculator software devs ask for anti trust laws when someone includes a calculator in their software suite?

Considering Microsoft got hit by the DOJ for this kind of bundling, yes. They've had to be very careful about including things in Windows.