Tenebrae is a modification of the quake source that adds stencil shadows and per pixel lights to quake. Stencil shadows allow for realistic shadow effects on every object in the game world. Per pixel lighting allows you to have fine surface details correctly lit. These are essentially the same algorithms as used by the new Doom game.
Tenebrae is a GNU General Public Licensed first-person shooter engine, one of the many Quake engines, it was created and is now mantained by Charles Hollemeersch . Tenebrae is available for Microsoft Windows, Linux and MacOS X platforms. Tenebrae means darkness in Latin.
Tenebrae2 only supports the Quake3 bsp format. If you want to make new levels in the Quake1 bsp format or use existing Quake1 levels you should use Tenebrae1.
It is notable for implementing stencil shadows and per-pixel lighting. The potential to use these rendering technologies in a PC gaming engine was already proven by their being known to be part of the game DOOM 3 (also by id Software), but the Tenebrae engine then became publicly available in late 2002 before this game was released.
A much improved version under the name Tenebrae 2 has been under construction since mid- 2003. Tenebrae 2 features major optimizations in the rendering engine (with extensive use hardware acceleration) and full support for Quake 3 maps (as opposed to the less feature-rich Quake map format). Although it is also based on the original Quake source-code, the Tenebrae 2 engine is capable of producing graphics which rival those of many modern closed-source engines (DOOM 3, FarCry, etc.)
A single-player game known as Industri uses Tenebrae as its engine.