Sometimes the biggest challenges come from games with very few rules. It's the principle behind sudoku and the driving force behind those sliding block puzzles with the numbers 1-15. In his latest game, Kurt Beig of Simple Machine has taken inspiration from both of these in creating Even Up, his new game for iOS and Android.

The object of the game is simple: slide all the numbered tiles together until there's only one left. You can only combine tiles with equal numbers, and when they combine, the number on the new tile will increase by 1. If you combine a pair of 2s, you get a 3, and so on. Tap any tile to see where it can go, and swipe to move it in that direction (or tap again to deselect it). That's all there is, and that's more than enough to keep even the most avid puzzle fiend busy.

Even Up features 125 levels of various sizes, and you get a star for each one you complete. The first few puzzles are easy enough, and as the game progresses, they become more difficult. It's a good thing there's an "undo" button. Passing each level doesn't feel like a chore, though: once you've unlocked a level set by earning the specified number of stars, you can solve the puzzles in any order. The interface is simple and bright, and moving tiles is a much more pleasant experience than it is with the metal 1-15 puzzles.