Flow Free is a Droid / Apple app that is easy to understand and progressively more challenging to play. It's great for all ages.
The gist of the game is that you have a grid of open spots. Placed on that grid are pairs of colored dots. So there might be two red dots, two green dots, and two yellow dots. Your task is to draw lines between each pair of dots so that no line crosses another line.
If you look at the image, you can see how it ends up being once you finish a level. This one, of course, is fairly simple. They give you a wealth of simple designs to learn the basics. As you go, they get more and more complex. Regular boards can go up to 9x9 grids, and if you have a tablet you can even get boards that go up to 14x14 grids. As you might imagine, those can get fairly complex!
You don't have to slog through all the easy levels, either, if you get the hang of it quickly. You can jump right over to the hardest puzzles and give those a go. You can have a fairly large board with all sorts of dots on it, and the lines will have to interweave in a pretzel shape in order to connect properly. It's a great logic puzzle.
The beauty is that anybody can get the hang of what to do. So an 8 year old has just as much fun as an 88 year old - and both are learning valuable logic skills.
The game doesn't have flashy animation or backgrounds or sounds. It doesn't need it. There's just gentle water noises as you solve the puzzles. Feel free to play your own MP3 playlist as a background :).
If you want to race, there are time trials where you can see how many small puzzles you can whip through in 30 seconds or other increments. While those are fun, I prefer the large, complex puzzles where you really have to think about what you're doing.
Well recommended for all ages of gamer, as a challenging, brain-testing puzzle that keeps those little grey cells active.
I acquired Flow Free with my own funds in order to do this review.