Grails comes pre-packaged with Prototype.js and Script.aculo.us out of the box.
In your HTML page header, include all of the necessary libraries in one line like so:
<g:javascript library="scripaculous" />
The default Grails layout (grails-app/views/layouts/main.gsp) includes a ‘spinner’ graphic which will display when any Prototype AJAX calls are executed. Grails natively supports Prototype in all of its included AJAX tags.