What you're looking at below is a piece of Iron Man concept art featuring a ridiculously badass piece of armor that was originally created for use in The Avengers. The art comes to us from Adi Granov, who posted some of the work he did on The Avengers and Iron Man 3 over on his Tumblr. He doesn't specifically say why this armor wasn't used, though we imagine it was created with a particular scene in mind -- perhaps a suit Tony Stark uses to help defeat Chitauri invasion, or a suit created to keep the Hulk under control. Or maybe it was for a scene in the script that we never got to see.
Nevertheless, it hasn't been used... yet. Maybe for The Avengers 2?
Here's a piece of art that Granov did for Iron Man 3.
[via Bleeding Cool]