Increpare has released two new simple browser games in rapid succession, each with rules left up to the player to discover: Promises is a brilliant little single-screen game that demands a mere 5 or so minutes of your time. Answer that demand. Negative Space looks like Tetris and controls like Tetris, but does not respond like Tetris.
If you only have time for one, do play Promises. As for Negative Space, it’s a neat idea but once figuring out how it works I didn’t have the patience to play it through to completion. The process of discovering its game-mechanic was satisfying, however.