Open Source Currency?

I've been wondering lately if there could be a way to develop a currency that isn't dependent on a nation. Obviously, in order to do that, we'd need something that people generally agree is valuable- like gold. The open source part of it would be the protocol and the form- the way the currency is fashioned.

Of course, like so many things, one sorta needs any illegitimate authorities in one's area to back off and let folks trade peaceably for anything like this to turn out. Unless it's an anonymous sort of thing. I've seen interesting attempts to do things on the internet, but there is a huge trust hurdle to get over before anything really good happens there. Any old con can put up a website, and so far the reputation/identity schemes I've seen are way too hackable.