For a true RAD tool with a visual interface, the only one I'm aware of (but have not tried) is Borland's Delphi for PHP; but it's not open-source.
As far as debugging, I think most of the major IDE's that support PHP can include XDebug and/or Zend Debugger. If you don't mind the cost, Zend Studio is probably the most comprehensive IDE for PHP out there. If you're cheap like me, you might take a look at Aptana Community Version (make sure you get the latest release candidate of the PHP plug-in beta, unless it's now been made the standard release.)