TWO YUMMY LIBRARIES! Ruby Facets is the single largest collection of core extension methods and standard library additions available for the Ruby programming language.
This widget displays a stack of images that you can flick through like a rolodex or a card deck. It uses gwt's deferred binding for the image generation and lightweight animation to create a fast and smooth experience in all supported browsers. Check out
XPath Checker is a Firefox Extension I wrote for testing XPath expressions interactively. You might find it useful if you use xpaths or want to learn how.