Valve's insanely popular Portal title has been unofficially ported to Android. Well, at least one level of the game has been ported to Android. Sadly, it's not Valve behind this project, so we can't say for sure if you'll ever be able to play a full version of the game on your Android phone or tablet. What we can tell you that the developers responsible for this port used the Unity engine to do it.
Android Police reports that "there's actually not much to play" and it's more proof of concept than anything else, but perhaps if we all cross our fingers and wish really hard, Valve will give us something we can actually work with. For now, this demo from a team of Russian developers is all we have. Savor all two minutes and nine seconds of it below. Oh, and in case you were wondering, Android Police says the choppiness you see is from their recording, and not the game itself: