Monolith uses the engine for their own games, but the Lithtech engine is also offered as an alternative for the Quake and Unreal engines, and is significantly cheaper.
The Lithtech engine was originally developed by Monolith for Microsoft, to be included as a 3D engine for use with Microsoft's DirectX, but that deal fell through. Monolith continued development on their own, and they have also licensed the engine to other companies.
The Lithtech engine is continually developed, and as of early 2004 the latest version is called the Lithtech Jupiter engine, or version 2.x.
The Lithtech 1 engine did not compare favourably to the more powerful Quake and Unreal engines, but it is lauded for the ease of programming in it. This is a direct result of its development history: because it was originally planned as part of DirectX programming in DirectX is extremely easy. Still, Lithtech games did not look as good as the competition, and lacked some features.
The Lithtech engine was completely overhauled with the 2.0 or Jupiter version: Lithtech Jupiter games can directly compete with Unreal- or Quake-powered games in features, and the graphics are at a comparable level. Lithtech Jupiter remains much more affordable for third-party licensing than the others.
Games with the Lithtech 1 engine:
Games with the Lithtech Jupiter engine: