Mister.Wolf: will also grant the 1st and 2nd titles of the Elder Scrolls Saga (Arena & Daggerfall
BlueMooner: IIRC the first two games can be freely claimed. Not sure where, but pretty sure they're free to the public now. There's also Daggerfall Unity, a recreation of the game (which I haven't played).
Indeed, they can be freely downloaded, and from the Bethesda website no less. Links below if anyone is interested:
The Elder Scrolls: Arena The Elder Scrolls: Daggerfall What the DOOM and Quake titles offer in particular is binding the two games to your GOG account, as they are unlisted here (it's mostly a matter of convenience, personally I was glad to).
Daggerfall Unity is a masterpiece of fan / community-driven effort (as is the still beta Skywind, a full recreation of Morrowind with the Skyrim engine, that includes new orchestral soundtracks recorded specifically for it). I have played the Unity version, and it is both a faithful remake in its regular form and so much more in the modded format... fully recommend it for a "fresh" experience! The work of communities never ceases to amaze.