Essentially, lets your users click a whole line of checkboxes by clicking the first and dragging down the line.
This is a crop-in script. That is to say, include it on your page, and you need do nothing else. Even primitive event handlers (element.onchange, for example) are supported, with no action on your part.
A demo of it in action is on my hosting: http://fordi.org/test/checks.php