http://bashdb.sourceforge.net/remake/remake.html/
remake is a patched version of GNU Make that adds improved error reporting, the ability to trace execution in a comprehensible way, and a debugger.
The latest version is based off of the GNU Make 3.82 source. We also have a some cool debuggers for Ruby 1.9, Ruby 1.8 (Rubinius), Python, GNU Bash, Z-Shell, and K-Shell.