Scratch

Warioware DIY is the latest game in the WarioWare series, announced at E3 2009. This game differs from the others by being able to create your very own microgames, and upload them to Nintendo WiFi connection for others to enjoy.

The microgame - maker, (as I like to call it:P) is actually quite advanced. You can chnage practically every aspect of the microgame. The background, the characters, the instructions, and the whole purpose of the microgame can be edited at will.
Want to drive a motorcycle down a highway while destroying obstacles? You can. Want to recreate a Space Invaders microgame? You can.

Warioware DIY is coming out on Nintendo DS soon. Discuss.
lol, I should be one of the E3 commentators