Newton’s Orchard runs a real N-body gravity simulation in the browser — build a solar system by setting each body’s mass, spin, axial tilt, and orbit, then scrub through deterministic time with a shuttle control instead of a play button. Distances are true to scale (an Earth radius is about 4e-5 of its orbit), so planet sizes are deliberately exaggerated just to stay visible. Complete three missions and you unlock the black hole. Free, MIT-licensed, browser-only, no account needed.