- script.aculo.us provides lots of cool functionality like visual effects, autocompletion, and drag and drop.
- Rico provides AJAX, visual effects, and drag and drop.
- Dojo is a large library providing many features, enough that it is available in different subsets (“Editions”). Included are AJAX, visual effects, and rich text editing.
- jQuery provides CSS and XPath selectors for accessing elements, among other tools.