In an Iwata Asks interview about the upcoming WarioWare DIY, Nintendo president and expert interviewer Satoru Iwata revealed a previously unknown codename for the system that would become the Nintendo DS: Iris. "Iris was the codename of a next-generation device we were exploring to succeed the Game Boy Advance-in other words, before development of the Nintendo DS," Iwata explained. "Eventually, it became a two-screen device with the codename Nitro, which went out into the world as the Nintendo DS. So, broadly speaking, Iris was the foundation for the Nintendo DS."

And surprisingly, Software Planning Development's Gorou Abe had been thinking about a WarioWare microgame creator since the DS was called Iris. WarioWare DIY has been a long time coming. Elsewhere in the (fascinating) interview, it's revealed that some of the included microgames were made by debuggers during the QA process, who made microgames as part of testing.
Source: Joystiq