This question already has an answer here:
Trying to get used to the whole windows 8 thing and don't appreciate the bipolarness, like a lot of people do. I've seen a lot of people try to fix this by making Modern apps windowed (using ModernMix or something), but how about doing the opposite -- making desktop apps modern apps? Being able to close them and switch them with the same touch gestures. That's the main thing.
So someone asked this for Windows 8 Force a non-metro app to run fullscreen outside the desktop?
It's been asked several times actually
Not sure if it's yet possible for Windows 8.1