Conductor: Musical New York Subway Map
Using data from the MTA’s public API, the piece displays train routes based on the official schedule of stops and departure times. Each line segment also turns into a musical note that triggers, if one line crosses over it (and will also sound a note if you tug at it, with your mouse).
Lovely, musical, and elegant bit of HTML5 + JS magic. A lot more wonderful detail about the project can be found on Chen’s blog.