There is an example of a programme that differentiates between long and short push-button pushes on the Arduino.cc website, but I was not taken it.

While you hopefully don't need one-button access to 911, a desk-mounted panic button is undoubtedly cool, and it makes for a great DIY Arduino project.

Thorin Klosowski DIY musical instruments are their own thing entirely, but if you're looking for a place to start, Adafruit has a guide to building your own MIDI controller using an Arduino.