Yes! And there are many other re-implementation projects, like OpenMW, OpenGothic, fheroes2, and others, which allow you to play the games if you can provide the original assets. Largely for older games, but the point stands.
PokeMMO is a online Pokemon Fangame that combines the first 5 generations of games. From what I gather, this is possible because it is up to the user to provide the ROMs, so litigious Nintendo cannot say they are re-distributing copyrighted material
This makes me think, is there one of those "awesome" lists for open game reimplementations? If not, someone should make one...
(edit: Thanks for the multiple great replies on this! Now I have even more stuff to go through to add to my lists, and I love having that problem)
That is impressive there is OSS Gothic 2
I wonder if its legal, how is it MIT