Coloured notes fall down four lanes towards a hit line near the bottom. Press the matching key as each note crosses the line. There is no fail state and no end, so the aim is to build the highest score you can before your combo collapses.
Timing is graded by distance from the hit line: within 15 pixels is Perfect for 100 points, within 30 is Great for 75, and anything else inside the 50 pixel window is Good for 50. Each hit also adds 5 points for every note already in your combo. Hitting a key with no note in range counts as a miss and resets the combo, as does letting a note fall past the window. Fall speed rises by 0.5 for every 1,000 points, and the spawn gap shrinks by one frame per 500 points down to a floor of 20.
No. There is no life bar and no game over, so a run lasts until you restart it. Missed notes only cost the combo.
There is no music. Notes spawn at random into the four lanes at a rate driven by your score, so it is a reaction game rather than a song chart.
Yes — on a touch screen the game shows on-screen buttons, and games played with a mouse work by tapping.