from http://openae.org/download-
BRL-CAD is an open source collection of software packages which was put forth into development in 1979 by the US Army Research Laboratory. The collection of libraries give the package the functionality to trace rays, interactively build geometry, image processing, signal processing, scripting, and graphics rendering.
BRL-CAD is open source and available for Linux, Unix, Mac OS, and Windows platforms in binary form (package already compiled).
To install it on Ubuntu Karmic 32 bit:
$ sudo dpkg -i libstdc++5_3.3.6-17ubuntu1_
$ tar jxvf brlcad_7.10.4_ia32.tar.bz2 | UN-ARCHIVES BINARIES
$ sudo mv usr/brlcad /usr/ | MOVE BRL-CAD INTO THE USR FOLDER
Thats it! To run MGED (the geometry modeler) portion of BRL-CAD you have to give a path dependent command like this:
$ /usr/brlcad/bin/mged
After the previous command, the two windows of MGED should appear.