This is the Windows Phone 7 Game Boy emulator. The dude in the video is showing off a ROM of Wario Land. We don't exactly care for the aspect ratio, or the button placement. Still, it must be fun for those who enjoy the classics.
It's not the first time we've seen smartphone emulators like this one, but it's probably the first one we've seen for WP7. Us? We are interested in checking out the eStore when the Nintendo 3DS hits, so long as Nintendo can keep up with the releases and give us the games we want.