A port of the atari800 8-bit home computer emulator to the DS and DSi consoles.
Once you download it, press L to access the emulator's menu.
On the DS, you should get about 65-100% native performance - frameskip can and will help! On the DSi, performance should always be at 100%. This is about 25% better than existing DS emulators for the 8-bit Atari computer line.