Live Query utilizes the power of jQuery selectors by binding events or firing callbacks for matched elements auto-magically, even after the page has been loaded and the DOM updated.
jRails is a drop-in jQuery replacement for Prototype/script.aculo.us on Rails. Using jRails, you can get all of the same default Rails helpers for javascript functionality using the lighter jQuery library.
A framework for creating e-books from Markdown/Textile text markup using Ruby. Using the Prince PDF generator, you'll be able to get high quality PDFs.