OpenMW specifically seeks to provide a new open-source engine for Morrowind. The proprietary game's original game assets/data are still required, but the engine is open-source and brings in new features while operating natively on Windows / Linux / OS X.
Among the improvements for the GPLv3-licensed OpenMW 0.19.0 release are implementing sleep/wait, further work on alchemy/potions support, and implementing several other in-game features such as death, spell creation, trainer window, skill increases from skill books, etc. Other fixes/changes include gamma correct rendering, NCC flag handling, and sound improvements.
The OpenMW 0.19 changes are outlined in this release announcement while embedded below is a video about this new open-source Morrowind release.