Ajaxit is a jquery script that helps updating a site with 
content retrieved content from the target of a link a user 
click.

Since the original recources of the download are not available 
here a place to download and fix bugs a fork of the code. 
Original development by ominds http://www.o-minds.com/

Original download: http://archive.plugins.jquery.com/project/ajaxit
Project documentation: http://www.o-minds.com/products/ajaxit
Drupal module: https://drupal.org/project/ajaxit