Most useful prototype / script.aculo.us plugins
Prototype is one of the earliest new generation javascript libraries (or javascript frame work) like jQuery & Mootools. Coupled with Script Aculous, it is a powerful library and many extensions/plugins are available for it. The one downside to this library is, it is rather huge and requires script aculous even for basic animations. Size is okay when compressed, but it is not easy to find a compressed version and if compress via javascript compressors, it might produce some errors.
Here is a collection of the most useful prototype plugins grouped in to categories so that you can find your script based on your needs. Includes scripts for image galleries, lightbox, in place editors, form validation, modal windows, image manipulation, auto complete, table sorting etc.
