[_pferreir_]

I asked myself the same question. At first I thought it was some kind of editor using the Stack Overflow Markdown flavor. It's really confusing.

[cruise02]

It is an editor using PageDown, the Stack Overflow Markdown flavor.

[danpalmer]

I still think it's a bit dodgy. If I used GitHub's form of Markdown for a similar project, I wouldn't think it acceptable to call it "MarkHub" and give it a logo of a Septocat in a black circle.