This is an attempt at exposing GIMP functionality as an XMLRPC web service.
This is not finished. It can probably not be finished that way it has been started. It will require a lot more code. Actually, putting GEGL behind such a thing makes much more sense.
Have a look at Xtns/Python to find the menu entry which starts the server.
But it works, in an extremely limited way. You can e.g. change the current foreground and background colors... See the gimprpctest.py script for an example.
To get an overview of what this XMLRPC server offers, point your browser to http://localhost:8000
And, of course, the buzzwords which make this a lot more understandable by the general public: Web 2.0, Web services, AJAX ;)