jRails is a drop-in jQuery replacement for Prototype/script.aculo.us on Rails. This brief description might not convince you to use JRails unless you are in any of these situations:

• You are upgrading your existing applications to Rails 3 just to disover that Prototype helpers that you have been using do not work with Rails 3
• You are a Rails developer and want to use a lighter JQuery library
• You are looking for a replacement of Prototype helper or Script.aculo.us

JRails allows you to use JQuery as javascript library on Rails platform. The latest release of JRails includes support for basic AJAX calls, RJS, observers as well as a limited set of functionality for draggables, droppables, sortables and visual effects. Support will continue to grow as the jQuery UI and FX libraries mature.