I just counted how many Doom games there are, apparently.
32 for personal computers.
13 for consoles.
... and WebTV Plus?
70 not counting UK/US separately, 115 total.
Counting UK/US only.
Not counting Trilogy (2001, 2004), Depths of Doom, Doom+Wolfenstein, Doom+Quake, any other combos, mappacks and not counting different publishers separately or releases such as Best of Infogrames, Platinum etc... and no shareware.
Only counting two registered Doom: standard and Australian.
Personal computers include PC, Mac, Acorn, BeOS, IRIX, Linux, Nextstep, OS/2, QNX and Solaris and is pretty approximate as I don't know anything about them and just took them from various lists.
Consoles include Atari Jaguar, Sega 32x, PlayStation, SNES, Panasonic 3DO, Sega Saturn, Nintendo 64, Xbox, Playstation 3 and Xbox 360.
Handheld includes GBA, Pocket PC and Tapwave Zodiac.
Digital includes id Store, Steam (not counting Doom Classic Complete or Doom 3 Pack), PSN (counting Doom Classic Complete as it's the only option there), XBLA, cellphones (Doom RPG only) and iOS.
And WebTV Plus, I've heard.