The DS software that would become the Mii Channel
The Japanese Wii site has a story where the developers of the Wii's Mii Channel are discussing the tale of the development of the channel, and shown within is a shot of the software originally built for the DS that was adapted into the Mii Channel

In the "Iwata Asks" series of interviews posted on Wii.com, EAD's Hisashi Nogami tells the story of the DS software: "For some of the Wii software I was working on, there were plans to enable the player to design their own character who would then appear in-game. Independently of those plans, there was a project to develop software for the DS that, in the same way, would allow you to design your character's face. You could then have fun exchanging these faces with others. One day, Iwata-san told me about this DS software and as I was so impressed by it, and it was so close to what I had been imagining myself, it ended up being adopted for use in Wii software. As we were working on making it into an independent game title for Wii, out of the blue it was decided that it would become one of the Wii system functions...and I'm still getting over that surprise!"