wspacegen is an interactive IDE for programing with whitespace (http://compsoc.dur.ac.uk/whitespace/). So it's possible to create .ws code relative easily and debug it as well. But attention, you'll addicted to it (-:
Excellent macro based library to see program flow, variables, timings, errors, warnings. "Must have" for C/C++ programmers.
Coffeetronix is the fast and simple Java UML workbench. It parses your java sources and creates an instant UML classdiagram.
JDebug is a simple yet powerful Java package for debugging and tracing of code in environments where other tools cannot be used. The modules included in JDebug will prove particularly useful to programmers of online service development.