Nintendo DS modding wiki

The Nintendo DS ("Dual Screen" or "Developers' System") is a handheld game console from the seventh generation of video game consoles. The console was launched in North America on November 21st, 2004 followed by Japan (December 2nd, 2004) and Europe (March 11th, 2005). The DS introduced distinctive new features to handheld games: two LCD screens working in tandem (the bottom one being a touchscreen) in a clamshell design, a built-in microphone, and support for wireless connectivity between DS' and to the now-defunct Nintendo Wi-Fi Connection service. The DS also supported backwards compatibility via a second cart slot for Game Boy Advance (but not the original Game Boy or Game Boy Color).

Three model revisions of the DS were released: the DS Lite — a slimmer and lighter model with a brighter screen and better battery; the DSi — a model that lacks backwards compatibility but has with two built in cameras, an SD card slot, access to the Nintendo DSi Shop; and the DSi XL — a larger version of the DSi.

See this GitHub repo for a decent listing of development-focused resources.