[m463]

also on GOG, DRM-free:

https://www.gog.com/en/game/the_zork_anthology

[thaumasiotes]

Not just those; Return to Zork, Zork Grand Inquisitor, and Zork Nemesis are there too.

(Zork Nemesis is pretty unlike other Zork games.)

[timbit42]

It's also DRM-free on my Commodore 64.