I just checked in a little project, I’ve been working on for the last couple of weeks.
It really begun at the last Copenhagen php-meetup; Joakim Nygård and Jacob Oettinger made a presentation of their project, WebCacheGrind. I casually mentioned something about having played with the dbgp-protocol (The debugging part of Xdebug) and that it ought to be simple enough to write a fontend for it. That prompted some snickering from the back row. Apparently some guys had this rule at their workingplace, that whomever said that something ought to be easy to do, had to do so himself. Not an unreasonable rule, I suppose. Obviously, I couldn’t let that go unattended, so I gave it a shot.
So what can spectator do? Mind that this is a first version and I really just meant it as a proof of concept. I think I got a bit further than that, but it probably still has a few bugs. Still, with the current version, you can step through a program, set breakpoints and inspect the stack. Really all you would expect from a debugger.
Of course, as some of you might point out, there are already other implementations available. Most notably Komodo, which is also implemented with XUL. However, these implementations are proprietary, and are integrated with an IDE, that you may not want to use. Spectator is an open source alternative and is IDE/editor agnostic.