Hi Christof, just wanted to let you know that I was typing a long reply, but managed to fuck up my ZETA session. Sorry for the bluntness, but I am not happy. In my reply, at the end, I came to the conclusion that you should start with a prototype. This is probably the best I can come up with anyways. If you look at src/tests/servers/app/newerClipping, you will find the prototype that lead to the current app_server design. Maybe you could start from that, but I don't know. Another important point I made, was that you should think about persistence of window setups. But if you plan to be able to combine windows of different applications, it will get tricky (who is responsible?). Anyways, maybe I find some time to reply again in more detail, or you can elaborate more on your plans. In the app_server, the classes you will need to touch are Decorator, Window and Desktop (for general window management). Some of the stuff that is currently handled in Window should be handled by Decorator instead (certain mouse events). It will get tricky if you want to handle different window types too (floating, subset, etc). But for a first prototype, to see if it really could work out, you can ignore it. Hope this helps and best regards, -Stephan