Has anybody thought about creating SudokuCoin? Instead of scrypt/SHA256 hashing, miners solve random Sudoku puzzles. The difficulty is the size of the board. Should be very CPU-friendly and hard for GPUs and ASICs.
Sudokus are a popular puzzle game and people can relate to that. So the coin should easy to market. Solving a Sudoku is a reasonable proof-of-work and easier to explain than hashing. It is also intuitive that something like a 121×121 Sudoku is hard.
Ok, there are few problems. For example, the difficulty of a Sudoku puzzle is impossible to estimate. So the block times would probably jiggle a lot. Technically, there are better ideas.
Nevertheless, it sounds like fun. You could probably gather some IPO money just for the fun of it. It would be hilarious, if somebody built this.