I know that with 1 wire and a file you can make the DS play GBA games...
Also with 1 wire you can link the Antenna up to the chassis and increase the wireless range...
The official PC emulator used for developer debugging is floating around...
Also there is something called a Magic Key that can rip the rom files from DS cartrages and write them back to re-writable cartrages....
This is all stuff I've heard in passing so I'm not sure how well any of it works...