Traditional bike safety lights mount on the back and look more like brake lights on a car, with variations being those LED lights you can stick on the wheels for Tron-esque side visibility. The Revolights, however, give you back and side visibility while being able to illuminate the road in front of you for night riding.
Here's a high level overview of how it works: Revolights attach to both wheels, detecting how fast your tires spin and only activating the appropriate LEDs so that you're always only blowing out light behind and in front of you (and not in your own eyes). When you're slowing to a stop, the light pattern changes to a safety-cycle, going around in a circle to show people that yes, you're still there, but just waiting for a light like a good cyclist.
Revolights are just a Kickstarter project now, but they've already gotten twice the amount of funding they need, and should start production when the design is finalised. The downside is that something on this scale and complexity will retail for $US220, so it's not cheap. But if you're a frequent night biker who wants to stay safe and look semi-futuristic, it's not a bad choice.