The Elder Scrolls: Arena
The Elder Scrolls: Daggerfall
An Elder Scrolls Legend: Battlespire
The Elder Scrolls Adventure: Redguard
(I've just played Daggerfall, but I'm very curious about the other ones)
System Shock 1+2
Both Daggerfall and Arena are available for free on their site, elderscrolls.com/arena and elderscrolls.com/daggerfall respectively, just need to get DOSBox.
Would love to see System Shock on here since I never got to play them and have heard nothing but amazing things about both of them.