This looks like a screengrab from Halo 3's Valhalla multiplayer map. But it's not. It is, if you take a closer look, actually a fully-functional PC desktop.
The radar monitors your outside temperature. The player indicators are links. The grenade icons launch programs. The ammo counters in the top-right show your unread emails and rss items. The health bar shows whatever music you're currently playing.
And neatest of all, the ammo counter on the battle rifle itself displays how much juice is left in your battery, should you use it on a laptop.
Rigging one of these desktops up isn't as hard as you think, so if this takes your fancy you'll find a how-to guide over at Lifehacker.
The Halo 3 HUD Desktop [Lifehacker]