Today I've been tinkering about with Tethernum - a game I found while following links from forums. Tethernum and its sequel, Tethernum 2 are simple but maddening puzzle games where you can change the colour of a block by clicking other blocks to which it connects. In each level you're trying to get all blocks to be the same colour.
In the first Tethernum you have two separate block boards to deal with. The blocks on one are linked to blocks on the other so it's a case of looking at what connects with what and then figuring out the order in which you need to fiddle with colours. It's a neat, simple concept but it's hard as balls.
Tethernum² works along similar lines but, instead of the sets of connected blocks being selected at random from the start of the game, you are changing the colour of a hex tile you're currently clicking and any which share a border with that tile. It's a bit easier to wrap your head around and to feel out the solutions.
Both were created by Eigen Lenk as part of Ludum Dare challenges last year.