Nimbus allows for switching between Pretendo and Nintendo Networks. To use nimbus launch it from the HOME Menu or the Homebrew Launcher, and select either Pretendo or Nintendo to switch between the two networks. While on the Pretendo Network, launch a supported game to play online with other Pretendo users.
Some features, notably Pretendo's Miiverse replacement Juxtaposition, will require a PNID to function. A PNID is a unique identifier, functioning the same as Nintendo's NNIDs. To create a PNID open System Settings -> Nintendo Network ID Settings. Alternatively, register for an account using the Pretendo website, and then link an existing PNID instead.