Question: I'm trying to split my application into different sub processes, each one doing a very specific thing. Main reason is stability and better memory utilization because i use a conservative garbage collector (boehm-weisser).

I don't want to do it one huge process that does it all. 

Unfortunately the subprocesses must display some windows so they will need NSApplication instances.

But i want them to appear as one application in Expose and leave the menubar of the main process when they became active.

Is there any way to do this?

Answer: 
I believe there's no way to do this (without **a lot of** hacking).

The only possibility which comes to my mind would be to have a dedicated UI process (which is the main Application) and do a lot of IPC to with the child processes. In short: splitting MVC over processes.
Isn't this what Chrome and Stainless are doing?

Having one GUI application which talks to several worker processes is pretty easy to do. Things will get tricky if you want those helper processes to present UI.

I could imagine having helper applications with no menu bar or Dock icon. There just might be an option to have those tack overlay windows onto the main application's window. I have never tried anything remotely like this though.