Multi-platform application launcher

I use an application that is multi-platform (Windows, Linux, OSX). I launch multiple copies of this application with different command line parameters. Each has its own window title.

I'd like to write a launcher for this application. I have a couple of questions. What is the best cross-platform way of launching applications from within Java? How can I tell if the application is already running? I can use JNA for Windows to enumerate all open windows looking for the title. What about the other OSes?

Are you talking about using a jar file as a way to launch an aplication?
Open a socket and use it to detect if another copy of the app is running.