Hmmm... where to begin?
This is the best CAD system I've ever seen.
While the interface is rather, er, esoteric, it's not hard to learn and the power of the system is unrivaled.
The description on freshmeat is misleading, both in the purpose and scope of BRL-CAD. The main reason for the structure of this package is twofold:
First, the desire to create realistic *solid* models rather than a "model" made from "sheets and boxes" increases the value of the model as a basis for real world use (manufacture) and realistic simulations including but not limited to those relevant to military use - neutron penetration, vulnerability to attack et cetera.
In other words, if I design my next homebrew helicopter in BRL-CAD (and I will) I can get real strength data for the rotors, frame et cetera.
Secondly, the CSG approach provides a POV (point of view - not Persistence of Vision) capability unmatched for scene rendering.
While obtaining this package is *very slightly* byzantine, it's very much worth the effort. Far more, in fact.
Oh yeah - the current version (as of 14/0119 April 2004) is 6.01, not 5.x.