"So what about Java Applets? There should be Java support for almost every platform. But then we're getting damn close to the jMax way of doing it... and they seem to try to get rid of their Java GUI for some reason."
Java GUI development is a bit of a time/resource eating monster. Not sure why - I've been involved in managing/working on a couple of projects recently with java GUIs and the GUI parts of the projects have just spiraled into huge jobs.
At the place I'm at now we are using c#.net which is not very cross platform
but very very easy to develop with. Not very suitable for pd though.
cheers
mark