Still Alive DS is a freeware game you can run on your DS if you have one of those evil, obviously only used for piracy, flash cards. Like an R4 or something. It’s a 2D sort-of remake of Portal, featuring the same sorts of puzzles, turrets, cubes and plasma balls, as well as the two-portal gameplay.
It’s a bit fiddly to control, and it doesn’t look all that amazing, but it’s a solid, clever puzzler. Unfortunately, I’ve now come to an impass, being totally unable to complete the level I’ve reached (29, I think). There’s a narrow shaft I have to fall down, but there’s a plasma ball bouncing back and forth in it, and I can’t time the drop to miss it. Bah.
If you want to play it yourself, you can find it here.