The Tenebrae project now has its own Wikipedia article.
Tenebrae is an open-source modification of the Quake engine that adds real-time per-pixel lighting and shadowing (stencil shadow volumes) to Quake. It was one of the earlier projects to demonstrate just how dramatically modern lighting could transform the look of an old game engine.
It's nice to see the project get some recognition in an encyclopaedia entry. Tenebrae had a dedicated community of contributors and served as a playground for graphics programmers interested in real-time shadow techniques during the early 2000s.