Bt Builder is an open source implemention of the Bard's Tale Construction Set. It is still very early in development. The file formats have been deciphered but no editor or game interface have been developed.
Questions or comments can be sent to dulsi@identicalsoftware.com.
Also check out the Open Game Source article that started development.
Bt Builder 0.1 (source tar & gzipped)
Identical Software Graphics Library 0.8 (source tar & gzipped)