Maps your QWERTY keyboard to a percussive bayan-style musical instrument. Built for the web with HTML/ProcessingJS.
You can try a live-demo here: http://michaelscottnelson.com/app/Charmonika2/
If you are musician and get a kick out of this, you can download a full-featured desktop app with additional features including MIDI in/out support, and a bank of synthesized button-box sounds. That version includes support for a variety of button-box keyboard mappings: Bayan-B, Bayan-C, Hayden, English concertina, Modal concertina, Anglo concertina, Early Wheatstone Duett, Wicki, and of course piano-style (accordion).