The phpanywhere site boasts itself as "the easiest way to bring work with you anywhere you go - without bringing anything". The free (still in beta) service offers online PHP editing through a web browser interface.

PHPanywhere is a web based free Integrated Development Environment or IDE for the PHP language, in other words it is an application that gives developers all the code editing capabilities they need to develop PHP applications online. It includes a real-time syntax code editor with support for all web formats and a powerful FTP editor.

You can add in FTP servers and pull files directly from them to edit and upload back over. You can also use the project sharing to allow others to see the current state of your code (real-time collaboration is "coming soon"). You can see screenshots of the editor interface, setting up FTP sites and modifying permissions for the files.