One performer, a guitar or a piano, and a room that gradually goes quiet without anyone asking it to.
A solo musician is the most versatile booking on this list. Acoustic guitar and vocals through a drinks reception, a pianist under the meal, a saxophonist lifting the mood as evening sets in, a singer with backing tracks that fills a floor and sounds far bigger than one person should. They read the room and shift with it, playing gently while people are talking and stepping it up when the energy wants to go somewhere.