jQuery

http://jquery.com/

jQuery is a fast, concise, JavaScript Library that simplifies how you traverse HTML documents, handle events, perform animations, and add Ajax interactions to your web pages

Conflict with scriptaculous / prototype

source: http://docs.jquery.com/Using_jQuery_with_Other_Libraries

Overriding the $-function

However, you can override that default by calling jQuery.noConflict() at any point after jQuery and the other library have both loaded. For example:

 <html>
 <head>
   <script src="prototype.js"></script>
   <script src="jquery.js"></script>
   <script>
     jQuery.noConflict();
     
     // Use jQuery via jQuery(...)
     jQuery(document).ready(function(){
       jQuery("div").hide();
     });
     
     // Use Prototype with $(...), etc.
     $('someid').hide();
   </script>
 </head>
 <body></body>
 </html>