From GameBrew - a wiki dedicated to Video Game Homebrew.
Neko DS is port of an old NEC PC application back from 80's where a cat will run around the screen and follow the mouse on screen. Neko is the Japanese word for cat.
It is released for the NEO Summer Coding Compo 2008 Coding.
When run, you would have a cat on your screen who would chase your mouse cursor around, scratch on the screen, take a nap and various other stuff.