The debugger is a wonderful, useful piece of code
I can see there are nice hooks to talk to the debugger from another process, but they're not documented. It would be great to be able to add a command or two to the debugger, but there's no easy way todo it other than copying the code, adding the command, and there you are. Of course, this is a maintenance nightmare.
Maybe I've found my subject for the Perl conference this year