Short form: It's a VR headset.
Long form: It's light enough and well enough designed that you hardly notice you're wearing it after a couple minutes. Stereoscopic 3D.
One of my friends here in OK got the dev kit for it and brought it to one of our gatherings. It was absolutely amazing. I have never encountered such well done 3D. The desire to go and replay all my old games on this is terrible. As a dev kit, the marquis game is Half-Life 2, but I have heard that someone got Portal working with it. The demoes I experienced were truly stunning.
http://www.oculusvr.com
Check it out. It's on my "must buy" list.
While you're at it, check out Eve: Valkyrie.
![Wink ;)](./images/smilies/icon_e_wink.gif)