For some time now, sound cards have been standard on PCs and the CPU has been quite capable of realtime audio processing. As a result, there are several free oscilloscope and spectral analyzer programs out there. Scopes used to be hundreds of dollars and spectral analyzers were very specialized large pieces of dedicated equiptment.
In fact, there are chips like the AD5933 which perform spectral analysis (analog network analyzer functions) in hardware, out to hundreds of kilohertz. But for kids eg learning about music, sound physics, or electronics, its amazing that they have this opportunity.
