The homebrew editor follows in the footsteps of the Pushmo level editor.
Eli Sherer released a homebrew Pyramids level editor for Windows today.
Pyramids is a 3DS puzzle-platformer by Enjoy Gaming, which is available for download on the eShop. The editor allows import and export of QR codes and functions similarly to Sherer's Pushmo Level Editor. The codes for extra levels were originally distributed by the developer, and no user-created level capability was available until now.
Sherer also posted a level pack and some technical information behind the level format. The editor is under active development, having been updated several times today.