BMRT is dead, long live... um, Aqsis or something.
BMRT was indeed one amazing piece of freeware. It could do a lot what commercial Renderman renderers could - even when it was slower and didn't come with as much shaders.
Regrettably, it was ruined in the war between its master and the master's old master...
BMRT was originally written by Larry Gritz as an aid for his Master's degree in early 1990s, and he later started distributing it to people. He was then hired by Pixar in 1995 to work on Photorealistic Renderman, but he kept working on BMRT. In 2000, Larry and some other people left Pixar to form their own company called Exluna, and in 2001 Exluna presented their own commercial Renderman-compliant renderer, Entropy (basically everything PRMan had, and about the same speed). In 2002, Pixar tried to catch up with Entropy on technological level with PRMan 11, and sued Exluna as a company and former Pixarians at Exluna as individuals for willful patent infringements and misappropriation of trade secrets. in July 2002, Exluna was merging with NVIDIA, and Pixar dropped the suit against Exluna and only sued these former employees for spewing the trade secrets.
The whole mess was finally settled out of court, but the end result is that Entropy and BMRT are no longer available to anyone from any of these parties. (I'm not sure if other people are allowed to distribute them, I have BMRT 2.6 Linux binary tarball somewhere here...)
(Source: http://www.renderman.org/RMR/OtherLinks/blackSIGGRAPH.html )