Yes, Mario Maker is real and it's exactly what we thought it'd be: a game that lets you create and play your own custom Mario levels. It's coming to Wii U next year.
You'll put down various elements like pipes and Goombas, and there's a toggle allowing you to also play levels in the New Super Mario Bros. art style. (Why?) Need to appeal to that new audience, I suppose. No word on pricing, but if it's affordable enough, this should make a killing.
Also, that dog icon from Mario Paint.