Macsbug code is all in the datafork of the macsbug "application". At least one version had a Mandelbrot drawing application in the resource fork (where 68k code and other resources live) so that it did something if you double clicked on it, but that was completely unrelated to the actual debugger functionality. Sounds like your macsbug has similarly been merged with some other application. You downloaded it from the internet? Give me the link and I'll have a look.

Ken