OpenMW is a free, open source, and modern engine which re-implements and extends the 2002 NetImmerse engine for the open-world role-playing game The Elder Scrolls III: Morrowind. Like the Construction Set for the original Morrowind engine, OpenMW comes with its own editor, called OpenMW-CS, which allows the user to edit or create their own mods or original games. Both OpenMW and OpenMW-CS are written from scratch, and aren’t made to support any third party programs that have been added to the original Morrowind engine to improve its functionality.

OpenMW is not a “mod” to Morrowind. It is an entirely different game engine that does not use the original executable file in any way.