Hacker News
This tiny script is a scraper for http://news.ycombinator.com. It shows just how little Ruby is required to run a powerful web filter.

What it be doin':
Fetches the YCombinator news page
HPricot's it into pieces
Builds an RSS feed
Uses links to parse the destination article page and include the main text inline
Runs as a stand-alone server thanks to Rack and Mongrel