chained-rails

https://github.com/tuupola/jquery_chained

Chained is simple chained selects plugin. It works with both jQuery and Zepto. Use class based version if you do not want to make external queries. It uses HTML class names of select options to decide content. To create selects from AJAX queries use remote version instead. This version makes an external AJAX query and uses the returned JSON to build child selects.