a minimal, easy to understand quick-thinking game
put your mouse (or finger) in the bottom left corner of the screen and hold it down to see the world record
drag the gem toward one of the numbers to add the number to your score (note: it only has to be toward it so you can drag past it or in it's general direction.)
don't let time run out or drag the gem onto an x
you get new gem colors as you get more points (note: hover your mouse over the gem indicators at the top to see how many points you need.)
the timer gets faster the longer you stay alive
you get 20 extra points if you drag your gem toward one of the scores highlighted by the blue bonus line

(CC BY-SA 2.0)