Roar is a notification widget that streamlines incoming messages, such as updates or errors, without distracting the user from their browser experience or breaking their work-flow by displaying obtrusive alerts.
Watir is a simple open-source Ruby-based library for automating web browsers. It allows you to write tests that are easy to read and easy to maintain. It is optimized for simplicity and flexibility.
SproutCore, a JavaScript framework that Apple has adopted for its own rich web apps, based on a Cocoa-like model-view-controller foundation with bindings, key value observing, and view controls.