Nintendo has shut down the Flipnote Gallery: World service for Flipnote Studio 3D on 3DS in Japan. The announcement of this closure was first made last September and the actual termination took place on April 2.
As the name suggests, the service allowed artists who used Flipnote Studio 3D to share their creations with one another. Despite it being called Flipnote Gallery: World, this service was only ever avaliable in Japan.
The main Flipnote Studio 3D software is not avaliable for purchase, but you can still access it via My Nintendo as one of the rewards.
Wonder if Nintendo might consider bringing a new version of this software to the Switch. After all, the system has a touch-screen: an even better one than the 3DS, at that.