This is an interesting project to keep an eye on if you’re looking to focus on a pseudo-native implementation of your Web app on OS X. If you’ve heard of Titanium before, MacGap should sound partially familiar.
In contrast to Titanium, which has seemingly expanded quite a bit since I last checked it out, MacGap focuses on making it easy to build a WebKit wrapper for your Web app.
It’s based on a fork of PhoneGap and definitely work poking around the source if you’re interested.