The library code and binaries can be found here.
I have included linux and windows binaries in the .tgz and .zip respectively for convenience. If you use the -p option, the program prints bc format operations and numbers so you can check things and follow along using the bc interpreter. You will need a bc modular arithmetic library such as this one by Anton Stiglic to do that.
credlib so far implements just the basic Brand credential features: issuing, showing with 0 to many attributes.
Note: Brands credentials are patented, and those patents are now owned by microsoft, however see below for the open specification promise from microsoft that grants some rights to use the patents.
In Mar 2008, microsoft acquired Stefan Brands credential patents
At the RSA conference in Mar 2010, microsoft announced the release of uprove a C# and java library implementing Brands private credentials plus formats and specifications under the microsoft Open Specification Promise which I think means you can now use at least parts of Brands patent suite, provided you conform to the interop guidelines set forth. And the guidelines are very reasonable for the basic protocol being something akin to DSA level of specification.
credlib is implemented by Dr Adam Back.