DBG is a full-featured PHP Debugger and Profiler. Makes it easier to find problems or bugs in PHP scripts. DBG supports back-tracking, watching variables, viewing arguments passed to all nested function calls at any point of execution. Opensource.
Denwer is a collection of often-used web-servers for web-programmers. It is used to debug web-sites under Win32. Denwer includes: friendly installer; Apache; PHP; MySQL; Perl; virtual host management system; phpMyAdmin; sendmail stub; start/stop manager.