HTML - Tagging

I am sorry if this is the wrong forum, but I did not see another place that this might be appropriate to post.

I am looking at sites that have tagging. Tagging is a series of links that show common search terms that people use on your site.

An example site that uses tagging is at http://www.boardtracker.com. Now they have their own software that they wrote that does this. What I am looking for is a 3rd party program that I can use on my website that does the same thing.

I have attached 3 pieces of a screenshot that shows what I am referring to on the above site. The first one shows the actual tags. If you click on one of them, it will perform a serch on the site based on that term. The second one just shows the search box and the category pull-down menu. The third one shows a text list of available categories and those link to everything that appears in that category.

Ideas?