Here's one interactive homebrew game for you and your friend on the DS. The Marshmallow Duel DS is POSPI's first DS game, but for a first timer, it's pretty swell.

So you got some hidden angst towards your pal? Invite to this game then. The mechanics are simple. Your goal is to push your friend into the water, so that you'll come out as the obvious victor. It's a deathmatch, this game. To kill your friend (that doesn't sound so right,eh?), you may choose to attack him on his other end of the screen, or you can use any of the 18 weapons that are randomly generated from above. I don't know if there's some kind of weapons factory up there, but the point is, it's giving you ammo, so no reason to complain right there.

The game itself can be viewed via the top screen, while the bottom part of the DS displays the scores and other knick-knacks. According to POSPI, the game's been intentionally designed to be very retro and so there's no real use of the DS's more unique features.

You can download the zipfile right here for the game, as well as the debug version, so that you can let POSPI know which class and functions are being problematic. He does admit, after all, that it's still in its beta stages, hence is still a little unstable.
He also plans to add wifi multiplayer, statistics saving, stylus menu controls, and stability and bug fixes.