Tweet Sentiments is mesmerizing, as it analyzes sentiment on the twitter feed. It uses OpenAmplify's Natural Language based Semantic Analysis engine to measure the positive (or negative) emotions associated with tweets. Watch as tweets roll by at a rate of 1 per second with the sentiment shown in red/yellow/green icons. Also has pie charts, gauges, and trending topic lists with associated sentiment.

Intridea is a leading web and mobile design and development company based in Washington, D.C. They specialize in web application development using Ruby on Rails and highly usable mobile applications for every major platform including iOS and Android. Intridea designed Tweet Sentiments as a showcase for their Twitter API development abilities. Worth checking out.