Doomdsay is Doom but it runs in OpenGL or Direct3D. I just downloaded this game and it's awesome. Doom in OpenGL looks surprisingly good. The resolution of the original Doom sucked, it was like 400x300 or something. Doomsday can run at resolutions up to 1600x1200 and it looks amazing.
If you own a copy of Doom, Doom2, Final Doom, Heretic, or Hexen, try this. It really looks cool
http://www.doomsdayhq.com/