So you want to build something using the Nifty API?
Here's the thing. It's brand new. Like, REALLY new. As of me writing this, there are only two applications using the Nifty API: this site, and the Firefox toolbar (which is being rebuilt now, so that one shouldn't even count). The facebook app is not using the API, because FBML don't roll like that. The API has not been "hardened" by lots of developers using it and breaking it and pointing out its flaws.
And I'm not using pre-rolled software - the whole thing has been coded from scratch from top to bottom. I've tested it in a hundred ways and it seems to be working great.
Still, if you want to use the API you'll have to be:
If you want to be the first person to build a 3rd party Nifty app, Contact me.