PHP has always had this hyper productivity about it. You just made a change in your editor, saved the file, and refreshed your browser for rapid feedback. It's always been like that.

It's also stateless - less rope to hang yourself with.

Many web programming environments started with the same simple CGI model, but eventually moved away chasing performance (for the computer), and leaving behind rapid feedback during development time.

hyperdev.com is nice, but it's still way more complicated than a single file PHP app.