Nintendo's surprise announcement during a recent Nintendo Direct, Mario Maker allows players to go retro and create their own original Super Mario Bros. levels to play and share with friends. It's a mix between the simple side-scrolling action of the very first Super Mario Bros. and a newly designed system which is really just a glorified map editor. Just imagine the stacks of goombas that can be made, though. Imagine it!
Mario Maker was apparently originally designed to be an internal tool at Nintendo to make additional Super Mario Bros. levels quickly. However, as it came together it became obvious that it held much more potential as a tool for players to easily create their own custom experiences.
The sharing functionality still remains to be described. Fans have expressed interest in sending custom levels to their fans, which is a reasonably simple request. However, they've also requested ways to collect levels and rate them, a feature that Nintendo has yet to tackle with its recent exploration into online functionality.