Pressy is a Kickstarter project and is basically a button which fits in a headphone socket and, with suitable software, allows the user to initiate tasks with single or double short or long clicks.
Just thinking aloud, could this be useful when used with the Raspberry Pi? Does the Pi headphone socket have all the necessary contacts? It would work with all cases, which would be quite handy.
Could it be a reset switch? Take a photo with the camera? An Off (mostly off) switch? Stop/start some application? Turn on/off WiFi?
What other functionality is the headphone socket capable of?