Impasse is a clever browser-based puzzle game in which the rules are never explained, although they're easily learned and understood just by playing through the first few couple of levels presented to the player. The objective here is basically to get the white circle to the light green one without touching any other circles along the way, but be warned - some circles move when you do, so you'll have to plan ahead to avoid contact with any of them while on the path to victory.

Each circle reacts in a different way when you take a step forward. Some will slide horizontally or vertically, while others will appear or disappear depending on your actions. Progress is saved automatically whenever you clear a level, so players can return to the game at any time if they need a break after attempting to solve a particularly difficult puzzle.

Impasse can be played over at Kongregate. (source: mirosurabu)