Just an idea: A Codeigniter Fiddle

A fiddle would be limited in capabilities, essentially, without a database connection to the live data, virtually every site I work on wouldn't be able to use it. Furthermore, any site other than our site, I wouldn't ever enter my logins for the database either (and setting up a remote schema and populating with fake data is possible, but then we're talking a lot of work to just use it and it gets beyond a fiddle, more like a truddery)