Homebrew developer [yaarglafr] recently released this video of his Protein DScratch in action. You can download a demo version here. The program simulates DJ scratching on the DS with an intuitive interface much like the ones on the touchscreen turntables we discussed the other day. It works well with any of the major DS slot devices; just run a DLDI patch on it and you’re good to go.
Aside from what is demoed in the video, DScratch can record and scratch audio directly from the microphone. It also has the ability to send midi data via the DS’s wifi, which in turn can be used to control external MIDI apps. Dscratch also has NDSMotion support. The DS slot and GBA slot DS Motion accessories contain accelerometers and gyroscopes that generate different effects in DScratch when the DS is shook, tilted, and turned. It’s not required for DScratch to work, but it maximizes the app’s functionality.
If you can’t wait for a full version, you can get the Korg DS-10 cartridge. Instead of emulating a turntable, though, this software emulates a Korg MS-10 synthesizer. It can handle music creation and editing like DScratch, but it cannot do midi controlling via WiFi. For that, try DSMI, an open source software suite we covered back in 2006. It consists of software for the DS that controls and sends midi messages via WiFi to the server software on a computer, which in turn feeds it to any running MIDI software. Neither of these do exactly what DScratch does, but they should keep you busy until the full release.