Ripple
An instrument disguised as a puddle.
The notes are a C major pentatonic scale across three octaves, mapped to how high you click — which is a fancy way of saying it will never sound wrong. Sound stays off until you ask for it, because nobody likes a website that makes noise unprompted.
On an iPhone the ring/silent switch mutes web audio on older versions of iOS. If the pond stays quiet after you turn sound on, that switch is the usual culprit; the volume buttons alone won't do it.