Flipnote Studio is a free DSiware application that has just been released all over the world on DSiware. It's a pretty deep animation program, with layers, onion skinning, different brushes, sound recording, etc. But the best feature is that you can directly upload your animations to
Flipnote Hatena, where you can rate and comment on animations as well.
Flipnote Studio also allows you to save your animations as .gif, so they can be used as avatars and stuff as well.
Anyway, I figured there must be at least a few people who have a DSi around here, so I thought "Why not make a Flipnote thread?"
I'll start it off with my 5 minute practice animation I did last night to get the hang of the app and its features:
http://flipnote.hatena.com/95850250F3FAF252@DSi/movie/FAF252_0908ECF3F5091_000?in=user