(Tenebrae = "darkness" or "shadows" in Latin) An interesting Quake mod that adds stencil shadows and per pixel lighting to the game engine. In less technical terms, this means that it adds more realistic shadows and lighting to Quake - every creature and item in the game will cast a shadow (no smooth shadows yet though), and the little surface details will also cast shadows (a bump map-like effect). Also, the game will have a little bit more realistic-looking water. This makes the game look considerably better.
This does, however, also mean it needs a fairly recent 3D hardware (any NVIDIA GeForce card is recommended) and considerably faster processor than the original (PIII-600 recommended). Also, you possibly need to mess with the maps to get optimal results.
The new version also adds even more features like particles (much cooler looking explosions and gunfire and smoke) and decals. There's even an approximation of soft shadows.
For me, Quake was always the horror-splatter experience. This mod would mean even more horrifying horror experience, and the screenshots certainly look perhaps even scarier than DooM! Certainly a gift from heavens for people who don't have the money to upgrade machinery for Doom III, and a very nice hack too... =)
Home page: http://tenebrae.sourceforge.net/