PhoneGap is a development tool that allows web developers to take advantage of the core features in the iPhone, Android, and Blackberry SDK using JavaScript.
Essentially, this utility will automatically package a Web App intended for Mobile Safari (or not…) into a native iPhone application. This may not seem like a big deal at first, but the real boon here is that there are hooks into the packaging system that allow the use of JavaScript as a bridge to call native iPhone APIs right from the web app. This means that a) you can write an application using your favorite web technologies and still have access to native API goodies like geo location, vibration and the accelerometer and b) you can charge for the app in the App Store.