I love me some portal, but I sure wish I could solve all of Aperture's mind-bending puzzles on the go. While the day when Portal because a portable title may well be a long ways away, this DS Homebrew by Smealum sure gives us an idea of what Portal on the Nintendo DS could be like. The mod is described as being "Nowhere near playable," at the current time, but the nifty video shows off quite a few staples of the franchise. Included are the Portal Gun, Energy Balls, and best of all, the Companion Cube!
"This is still extremely early footage so please don't be too harsh. Lots of debug features are present, including the ability to fly, see portals through walls and move cubes from a distance. Also, keep in mind this was shot in an emulator which provides good but still less than perfect rendering. As such, be aware that most (not all, but still) of the graphical glitches you can see in this video don't happen on hardware (mostly the portal transition is a lot nicer on an actual DS)."