With the Flex SDK out, were no longer restricted to use the Flash IDE to compile ActionScript. So i thought, what can I do with that? I don't need another environment for my AS other than Flex Builder. So I thought, why not on-line? Compile actionscript in your browser! So I went working on it, and actually its very very easy. It just needs like 4 lines of PHP and the Flex SDK on your server.
Source is available here: flexphp
Mr.Doob: Be aware of some scurety issus, like using ExternalInterface for bad, or doing embed[""] of files in the server... stuff like that...
As you can see its really simple. Just point to the sdk folder and the AS file. Only thing that remains is getting the chmod right.