Wikipedia
OpenMW is a free, open source and modern game engine which reimplements the one that runs the 2002 open-world RPG Morrowind.
OpenMW does not recreate game assets, such as art, textures, music, and other Bethesda copyrighted material. It is therefore necessary to own a copy of Morrowind to legally play the game with OpenMW. There are however existing free assets such as the OpenMW-Template project which gives game developers a working base for creation of their own game. Another project exists, OpenMW-Example-Suite is a free and DFSG compatible stand-alone game which will be used to demonstrate what OpenMW is capable of. It is also possible to operate the OpenMW-CS tool without the need for any third-party assets.