You can use SwingOSC: http://sourceforge.net/projects/swingosc/ You can build java GUI and control with osc messages. It is weel integrated from inside the SuperCollider language, but it is reported to work weel with PD also.
2010/6/30 András Murányi muranyia@gmail.com:
The 909 emulation was nice, but i couldn't make it work on Linux. (not only Pd but Processing was needed too). So, you can always control Pd from an external GUI using network messages, but you have to do it smart to keep it platform-independent. Web-Pd is a project i'm very interested in - when it gets vanilla functionality, we'll have a chance to fabricate wonderful GUIs while staying in the browser, which means staying platform-independent (eventually browser-independent too).