Something which resembles a lava lamp crossed with a VU meter, this ferrofluid bluetooth speaker is the result of many hours in the lab - and yet another brilliant Arduino based project. Youtuber DAKD Young has made numerous videos to show the workings of his floating musical blob, with various genres of music.
It's a pretty transfixing watch. which reacts naturally to transients in the music as if suspended in zero-gravity. Oh, and for the record, if you want to know where the term BlueTooth came from, Tom Scott has the answer.