Rock Garden Deluxe
Things could not be easier: you have to herd all of the identical stones into clusters, at which point they will flip over with the uniform efficiency of a Mexican Wave. The trick is getting them together. A stone is flicked into a direction and it will perpetually travel until it hits a boundary or obstacle. A board with one or two stone types is relatively easy to crack, but when the game starts to hit four it gets tricky. Every board is shaped differently, both on its boundaries and inside, making the shuffling a more deliberate endeavour. You have to maneuver a stone around bends, past other stones and into its own group. but once a set of stones has flipped, none of them can be moved. So you have to keep your end game in mind and not accidentally corner a stone beyond redemption. That just causes stress...
At first glance it seems the trick is to finish a puzzle with the least number of moves. Instead, Rock Garden measures you by speed. There is not limit on how long you can take, but the closer you get to the stage's best time, the more stars you get. Beat or equal it and you get the full five, plus from Level 15 onwards you can win a special stone from selected levels. These stones go towards your collection, which is a trophy room of sorts, plus they expand the collection of stones you can use in the very Zen 'Your Gardens': custom levels that seem to only be about placing and flicking around stones. If you prefer a slow game, but with an actual point, you can try out the random level generator. It still keeps time, but no high score.
Rock Garden Deluxe is a strange breed, because it is peaceful to play and yet turns into a thoroughly challenging puzzle game where you learn to think a few steps ahead. This is the full game with 100 levels and a commercial version is also available to buy. Whichever you choose, flicking around stones with little care in the world has never felt more rewarding.