95 and 98 were 4.0; NT4 was, well, NT4; ME was 4.1; 2000 was NT5.0; XP was NT5.1; 2003 was NT5.2; Vista was NT6.0 at the release, with SP1 it got the kernel of 2008; 2008 was NT6.1; 7 is NT6.1 (they claim it's internally NT7, but they kept 6 in the reported version number for compatibility).

So... they should name it Wintendo 10