For some time I've been messing around with some homebrew stuff for handheld platforms. I'm incredibly impressed with how far it has progressed with things like devkitPro which is a user-friendly collection of some of the reversed-engineered SDKs that are available for different platform and easily rival the official versions.
Especially the handheld platforms really intrigue me since there is a lot of potential there for new types of games and applications. Colors! is a program I've developed that I released a couple of weeks back that are along those lines. It's more or less a digital sketchpad on the fly, which I'm currently having a lot of fun with.
I'm going to talk a bit more about handheld homebrew in general, but if you want to check out Colors! you can go here.