Well, I’ve been accepted into the Google
Summer Winter of Code. My proposal is to build a GUI frontend for Xdebug‘s debugging functionality — and to answer a question I’ve already been asked on IRC, I’m currently planning on using wxWidgets as the GUI toolkit.
For the record, the abstract is:
Xdebug  provides a range of useful functionality for PHP developers, including detailed error information, code coverage and profiling support, and support for remote debugging using the GDB or DBGp protocols. At present, there are several DBGp implementations available as part of larger IDEs , however there is currently no standalone GUI application that can be run to debug applications using DBGp without tying the developer to a particular IDE.
Under this proposal, a cross-platform GUI application will be developed that implements the DBGp protocol to allow PHP applications to be debugged using Xdebug in a development environment agnostic fashion. This application could then be further developed to include support for other run-time environments that support the DBGp protocol, which includes Python with Komodo  and may also include Ruby in the future .
I’m really looking forward to working on this, and will doubtless blog about it as development gets going. Thanks to Google, the PHP developers who selected the projects, and Derick, who’s going to be the mentor on the project.