RINGO was one of the first collaborative filtering systems (MIT Media Lab, 1994). Unlike content-based systems that match song features, RINGO finds other users whose tastes match yours — then borrows their ratings for songs you haven't heard. Rate songs 1 (hate) → 7 (love) and watch the algorithm recalculate in real-time. The more you share with a neighbour, the more their opinions shape your recommendations.