[prokoudine]

Neither Fusion nor SolidWorks mention supported operating systems on their respective homepages. That doesn't seem to present an issue, eh? :)

As for your other points, FreeCAD's homepage does explain what this software can do. It says what this software is right on the first screen. You can scroll down past the first screen to see more info. Even more info is on the Features page that is right in the main menu at the top.

I mean, we can argue about the amount of information, but the basics are all right there for you, in very obvious places, no?

Incidentally, a new (and better) website is in the works.