Shown at Comiket 80, "Tiny Trek" is a remake of the 1971 Star Trek text game for DS, made using the Japan-only, DSiWare-released coding program, Petit Computer. It's pretty amazing what's been done with the program; I've seen a few doujin shmups and RPGs that use it, but using it to make full-on text-only games is pretty surprising.
I can't imagine writing all of that code on a DS screen though.