Underground Music Speaker
Have a speaker in a public place above ground playing music live from a street musician underground. Also have a donation box.
Data input: sound from musician underground
Data output: sound through speaker overland
Would people dance to a speaker? Would people donate without being able to prove? Would people donate to a speaker? Does the physical body of a musician matter?
Further design: Have speakers outside of an expensive concert play music live. Create a barrier and charge people at the entrance. Charge a fraction. Would people pay?