Windows 7 on my desktop, mostly because I haven't upgraded to 8 yet (Still holding out hope I might get Zoo Tycoon Ultimate and Neverwinter Nights Diamond to run it ><; ). My Surface Pro 2 came with windows 8.1, and all the rest of our computers are 8.1 as well. My husbands messed around with Ubuntu some, but I don't know anything about that really.