Meet the SmartScope from LabNation: a gadget that turns your tablet, laptop, or smartphone into an oscilloscope. It is compatible with a variety of platforms. The SmartScope comes with 4 digital inputs, 4 digital outputs, an arbitrary waveform generator, and everything you need to get started.
You will need a single cable to start using your smart device as an oscilloscope. This could prove useful to Arduino / Raspberry Pi developers and other makers.