bwtzip is an ongoing project, distributed under the GNU General Public License, to implement a Burrows-Wheeler compressor in standard, portable C++. It is research-grade in that it is highly modularized and abstracted, so that it is simple to swap out parts of the compressor without affecting anything else. This makes it easy to experiment with different algorithms at different stages of compression.

Looks like Steven T. Lavavej released a new version of bwtzip in early February, 2003. A wide variety of improvements, most of them in implementation - not visible to the end user. A description of recent changes is found here

http://stl.caltech.edu/bwtzip.html