The Pebbles game has two main challenges.

The first challenges are the NxN -1 sliding puzzles including the 8-puzzle, 15-puzzle, 24-puzzle, and so on. These puzzles have classic modes as well as expert mode and time based challenges. The expert mode and time mode are very smooth and really fun/engaging!

The second challenge is a variation of the 15-puzzle that requires the player to either flip two tiles or build a circle of tiles that would rotate synchronously. This is a tough puzzle if you want to get three stars! In the first release, 16 stages are releases. More stages will be released in the future.

Best of all, the game is completely free. Hope you like it!