One example that appears to be a free market success, but I can give anecdotal evidence where is would not have been is Microsoft.
While true that Microsoft achieved market dominance, it was never a "monopoly" in the economic sense, that it could charge "monopoly prices" without competition, or in the literal sense of having a government mandated sole-provider status (such as "Major League Baseball" has).
In the 80's I worked for a corporation that did government contracts. All of our documentation was in troff/nroff until the government required us to deliver our documentation in Word (or whatever Microsoft had at the time). I heard from friends in the industry that ALL companies received the same requirements - deliver documentation in a Microsoft proprietary format.
Govt procurement -really- drove Windows adoption. It was much easier on a govt requisition form to say "Windows PC" than to specify all the details which would be needed to specify anything else. And providers such as Dell, Gateway, and Compaq, could get the product very quickly.
The predominance of DOS/Windows did do one very good thing, it brought standardization to the commodity market. Prior to that, my TRS-80 couldn't share files with Jim's Commodore-64, and so on.
I realize that the idea of cross-computer compatibility was no mystery to the UNIX users of the world, but before Linux, UNIX was an esoteric tool which required both a "real" computer and serious experience/money to acquire.
The explosive growth of "The Internet" from its release in early 1993 to the launch of Windows95 (which didn't even have TCP/IP, email, or a web browser) was due, in part, to the success Microsoft had in already getting people accustomed to the idea that anyone could share files with anyone else anywhere.
Can you imagine having the power to lock in millions of people into an O.S.? I believe that is why Microsoft was so successful in the 'free market'.
Microsoft would have been successful even without various govts requiring DOC formats, or buying millions of computers just for government use.
But I expect, just as they wrote Word for the Mac, Microsoft would have had much more incentive to make their software available to run on many different platforms, rather than trying to lock people into "Windows" itself.
It is important to note that Linux started in 1992, had a very standard GUI with the Xwindow system, web browser before Internet Explorer existed, etc etc, and all those same things were running on other UNIX variants. Apple's Mac also had everything Windows did before Windows did, but was overwhelmed by the effects of inexpensive hardware not being able to run MacOS.
It's never been a requirement to run Windows or use Microsoft software, but there were times when it was simply so much easier to do so than to try to do it any other way.
Note: I've never bought Windows other than pre-installed on a new PC, and I don't have it on anything but my work system because they require it.