Not that I know of, but it's a pretty trivial app. It just removes all of the default routing. Sure, I could probably add them back, but I've intentionally never learned how to use the BSD route that comes with Mac OS for that reason. :-)
With Linux, actually, you could probably go one level lower by writing a small kernel driver that you could signal from user space to disable networking for a given period and then do some goofiness so that it couldn't be unloaded effectively and still get networking back.
