Forum OpenACS Q&A: Re: Charles Web Debugging Tool
But it is nice and general, i.e. it works as a proxy and so can help you detect all sorts of problems to all sorts of site. And what's kind of nice about it is that you can run it either at your own workstation OR on the remote server. I'm a bit put off by the UI and the $50 shareware fee.
If you're just looking for something similarish on AOLserver, my mods for AOLserver 3.3 add hex dumps of all requests to the log -- that has been terribly invaluable for me in debugging new protocols at times.
I wish I knew of a similar mod_dump_hex or mod_log_all or something like that module for Apache....