There's nothing stopping you from running multiple JRuby instances, just as you would with any other interpreter, it's just you can't use fork() to create them.

There's nothing stopping you from running multiple JRuby instances, just as you would with any other interpreter, it's just you can't use fork() to create them. Use an external script/daemon to start up multiple processes. It's not as memory efficient as MRI, but isn't _too_ bad unless you're on a cheapo memory constrained VPS.