It’s not exactly an advertised feature when a game is DRM free on Steam, so this list may not be comprehensive or accurate for every game. DRM is optional on Steam. You can copy these game directories out of Steam and run them on a totally separate computer with Steam not even installed, and they’ll still work.
And I’d have just made my username &rew if they let me, but this is the one I use when that one is taken or they have limitations on special characters. With the special character, it has the benefit of fitting in old-school four character clan tags as well as Smash Melee names (and I don’t like going by Drew).