I just learned about Underworld Adventures, an open source engine recreation project for Ultima Underworld which seems to be quite obscure for some reason. It was indefinitely suspended in 2007 but a quick check suggests that the latest build is quite functional. It supports both the full version and the demo. The project also includes a high-quality music pack.
Some screenshots:
Underworld Adventures - Ultima Underworld engine recreation
A visit to the Ultima: The Reconstruction website revealed a few more engine recreations of Ultima Underworld:
o Abysmal Engine
o The System Shock Hack Project
Both aim to support System Shock as well as UU, and both appear long abandoned.
o Abysmal Engine
o The System Shock Hack Project
Both aim to support System Shock as well as UU, and both appear long abandoned.
Underworld Adventures - Ultima Underworld engine recreation
Looks like the project is still being developed, it has moved to a new site and an update was released in 2021:
https://vividos.github.io/UnderworldAdventures/
https://vividos.github.io/UnderworldAdventures/