Here's a really neat video puzzle game that you can play online for free in your browser. On one level, it's a relatively simple idea. There's a person, a key, and a door. Move the person to pick up the key, then reach the door and you've completed the level. Of course there are a few obstacles in your way, but they're pretty easy to scale with a jump.
What makes this game especially novel is that the playing area is actually split into 3 separate windows, and you'll need to manoeuvre your character between the windows in order to complete the game. Which means stopping the action at key moments and moving the windows around, so that the character can pass into a suitable space rather than a dangerous drop or void.
It makes a lot more sense once you start playing, and is very easy to get the hang of. All you need are the 4 arrow keys to move around, and the space bar to switch between play mode and window shuffling.
Give it a try by heading to http://continuitygame.com/playcontinuity.html and you'll see just how clever it is. Even the background music is pleasantly calming.