Here is a nifty web app: tRuTag
I’ve created tRuTag with Ruby because I wanted to explore tagging. What it does is create an html page of your tags on various sites and then allows you to explore them on other sites.
I use it as my homepage and have just implemented some of it’s functionlity on my Ruby on Rails site. Below is a sample page. Please view the readme or download tRuTag and enjoy!
It requires Ruby on Rails to run. I’ll probably try to get this set up on my laptop this weekend.
(Via O’Reilly Radar.)
C. David Gammel, CAE 
Thanks for the link. Actually tRuTag does not require Ruby on Rails to run, though I have made a basic demo on rails here http://rubyyot.com/tag
It is written in Ruby so you will need Ruby to run it. To find out more about Ruby or download it if you do not have it installed please visit http://www.ruby-lang.org
If you have any other questions please feel free to ask. 🙂