Blood Technology..

Building on the Build.

Build, the powerful 3D Realms game engine written by Ken Silverman, boasts some of the hottest features available in a 3D game:

Sloped or slanted floors and ceilings, allowing levels to have interesting and realistic architecture.
True rooms above rooms and real bridges.
Moving sectors that can be made to rotate, incline, and move in numerous other ways, making for a dynamic, realistic, and often dangerous environment.
Multiple colors of light.
All sprites and game characters cast realtime shadows, adding to realism and anchoring enemies in the environment.
Head canting, clockwise and counterclockwise, a full 360 degrees.
The ability to look up and down by about 40 degrees each way.
Many X mode and SVGA resolutions supported.
The Mapedit level editor, a significantly enhanced version of
Build, is extremely powerful and easy to use. It allows for fast editing in both 2D view mode and 3D mode.
The 3D editing mode allows level designers to see what they're creating in real-time—including lighting effects and z motion positions (i.e. you can open and close doors).
Parts of the environment can be destroyed or otherwise affected during gameplay.