OpenMW is a free, open source, and modern engine which re-implements and extends the 2002 Gamebryo 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 Morrowind.exe in any way.
More information can be found via the FAQ at the OpenMW website.
You may also follow the project via the OpenMW Github page.