BSP is one of the best node builders for Doom.

What are Nodes?

Doom uses a rendering algorithm based on a binary space partition,
otherwise known as a BSP tree. This is stored in a data lump called
NODES in the WAD file. So tools to build the BSP tree are known as
node builders.
   
Before you can play a level that you have created, you must use a node
builder to create the data that Doom will use to render the level. BSP
is one of several node builders that can do this.

WWW: http://doombsp.sourceforge.net/

- Christian Brueffer
chris@unixpages.org