Whiteblade999: Fun fact: All the ID games that use dosbox on steam are DRM-free. Even better is for Heretic, Hexen, Hexen: Deathkings of the Dark Citadel, Doom, Doom II, Final Doom and Master Levels of Doom all have content files which can be used in source ports which make the game look better, play better (mouselook or jumping in all of the games), and perform better.
Edit: Same aplies to X-com, I'm not sure on any others.
Some of the older LucasArts Star Wars games are also like that, Dark Forces for sure, maybe others as well.