It works perfectly. Just click a different toolbar and a different window is opened, in the case of Projects/Files/Services. Compare that to the default, where you have tabs instead:
It's not very easy to do something like this. In this case, the class that did the trick extended AbstractTabDisplayerUI. It would be cool if somehow something like that could be done to add new buttons to the toolbars of TopComponents, though I'm not that far yet. Even better would be if there were different window layouts that the user could select.