Westwood Studios made quite a lot of games like Dune II and the Command & Conquer series but they also made an RPG called Nox, that now lives on with the OpenNox game engine. OpenNox just recently had a new release, and the project is now open source too under the GPL!
Released originally in the year 2000, Nox was received very well by the gaming press at the time and lives on in the hearts of many gamers. Thankfully now though, OpenNox gives you a fresh way to play it on modern platforms like Linux and Windows. OpenNox is a fully-featured game engine reimplementation too supporting the original features plus plenty of enhancements including: improving modding support, higher resolutions, much better online play and more.
Like other open source reimplementations, it does not include copyrighted assets and so you do need to own a copy of the game to play it which you can buy on GOG.com.