A programmer by the name of T4ils has released their own 2D remake of Valve's Portal, so anyone in the homebrew scene can play it on their DS. Titled Still Alive DS, it's minimalistic, sure, but it's Portal! As a bonus, a map editor is included, opening up the game quite a bit more. Check out the video:
Much like the PC game, players must rely on their wits (and a portal gun) to transport themselves around each stage, aiming shots with their stylus and grabbing pieces of cake along the way. It might not have the graphics of the original, but it definitely has the feel and charm.