OpenMW is an open-source open-world RPG game engine that supports playing Morrowind. Main repo and issue tracker can be found here: https://gitlab.com/OpenMW/openmw/ - OpenMW/openmw
A couple of us were talking about this in IRC today. Planning on giving it a try this weekend.
Fun fact the sdf lemmy has an openmw community: https://lemmy.sdf.org/c/openmw