OpenMW is a free and open source engine for The Elder Scrolls 3: Morrowind. It aims to be a fully playable and improved implementation of the game’s engine and functionality.
OpenMW is released under the GNU General Public License version 3, and all source code has been written completely from scratch. It also builds on various other open source tools, most notably OGRE for graphics, and Bullet for collision (and possibly physics).
OpenMW developers are doing great job as the engine is looking more and more polished with every new release and it works quite nicely on Linux. You will need the original game data to play OpenMW. OpenMW runs on Windows, Mac OS X as well.