The Sith Engine was a game engine developed by LucasArts. The game Star Wars: Jedi Knight: Dark Forces II was based on that engine, and its expansion, Star Wars: Jedi Knight: Mysteries of the Sith, on a slightly updated version.
Updated and altered versions of the engine can also be seen in Star Wars: DroidWorks, Star Wars: Episode I The Phantom Menace video game, and Indiana Jones and the Infernal Machine.
It was also imported to Grim Fandango, as a part of the GrimE engine.
It does not support per-color transparency, and has a Nintendo 64 level of anti-aliasing. It renders with ease, however, though the background environment and the gun in the first person view tend to be on entirely separate rendering layers. The background would run at 30 FPS, whereas the gun would render with no framerate cap. Though this caused no problems in gameplay, more modern computers tend to play on-screen weapon animations too fast, due to the fact that they are much more powerful than their 1997 counterparts.
3do files are the 3D models used in the basic Sith engine. Each one contains texture definitions (called MAT files), and text that details mesh names, vertices, faces, how they are shaded, and the like. MAT files are converted 256 color bitmaps. These bitmaps can only be rendered in perfect squares dividable by 8. Since merging all of the textures into one file was very much not feasible (until more recent methods of assigning textures to fan-made 3do models were discovered) each individual body part has a different texture. In some cases textures are reused.
The 3do models' animations come from files called KEY files. Although they share the same tag as Windows' registry, they are far different. KEY files are animation definitions, as every frame of the player's and enemy's animation sequences, as well as sometimes even ships' flight paths' are defined in these files. Extensive modifications to KEY files can create entirely new motions for characters, though in some cases an enemy's KEY files and the player's KEY files are not interchangeable.