OpenMW - An open source port of TES3 engine
An open-source "The Elder Scrolls III: Morrowind" engine reimplementation
OpenMW is an excellent version of Morrowind and arguably probably the best.
It’s crazy how good this is, from a software engineering perspective I have no idea how they pulled this off. Morrowind is such a complex game, not sure how they reverse engineered it.
Time. This is a very old project. Things have moved slowly, but with time, things starts to actually work well.
This is a perfect example of what FOSS can do compared to money-oriented development.