Homebrew Crayon Physics for the DS! Works great, although the code is a bit buggy (froze up my DS a few times). Not really a game yet, more like a physics construction kit. Still, it's a nice tech demo and proof that DS can handle a Crayon Physics Deluxe type game. Bring it on, developers!
Here is an interview with the maker of Pocket Physics where he talks about the challenges of getting it running on the DS (sounds from the comments like it doesn't work perfectly yet, but it's getting there).