Twenty

Twenty is a colorful arcade/puzzle game that starts at 5, looks easy until 10, gets fiendish at 15 and challenges you to get to 20. Anyone can learn it, but you'll have to concentrate to make it all the way. Think you've got it mastered? Try one of the variations like Bubbles, Drop, Flip-Flop. Try Zen mode to relax, or Panic mode for a real challenge.