Transit Trainer is a puzzle web app that helps you learn the NYC MTA subway system.
I hacked on Transit Trainer at the Google HTML5 Web App Hackathon. We were able to build a pretty decent app in 5 hours. The web app has a few layers on a canvas. We started with a blank Google Map, then overlaid the MTA subway lines, then overlaid the stops. We use a lot of the features that HTML5 has to offer including some details such as Google Web Fonts.