Every now and then on the internet someone comes up with an idea that is so absolutely fantastic, but so amazingly simple that you wonder why you didn't think of it first.
Although technically speaking flash games don't necessarily need to be confined to the internet to have success, this game has spread like wildfire over the internet, even to the point that the official site for it now seems to be, at the current moment, crumbling under the pressure.
What I am talking about is of course 'Line Rider' (official site: http://www.official-linerider.com/). The game is simple enough: draw some lines, press play, and a little dude on a sled will 'ride' your lines.
Now on YouTube there are thousands of people showing off their own tracks and all the nifty and amazing things you can do with jumps, somersaults, and crashing the guy at speed into a wall.
If you can find a site with enough bandwidth to actually show you the page to play it, I highly recommend you give it a go, it's awesome fun.