It's working with Carnegie Mellon University on Reconfigurable Wheel-Track technology that converts wheels from tracks to tires (and vice versa) in the middle of a drive. As you can see in the clip below, the change takes just two seconds — you could drive off the road and up a hillside without skipping a beat.
DARPA has been showing off RWT as part of a series of vehicle research projects including an in-hub electric motor (to improve speed and maneuverability) and Multi-mode Extreme Travel Suspension (to allow high speed over rough ground). It's looking into technology that improves drivers' awareness, too, such as virtual windows (enabled with 3D goggles), sensor-enhanced virtual perspectives and visual overlays that help find the quickest, safest route for off-road trips.
The transforming wheels are a long way from reaching production vehicles. DARPA is still in the midst of phase two of a broader Ground X-Vehicle Technologies program developing RWT and the other hardware you see here. With that said, the practical uses are more than a little obvious, and not just limited to military uses. While this would be immediately helpful for armored vehicles that need to cover ground as quickly as possible, it would also be helpful for search and rescue, construction and any other situation where there's a mix of flat roads and unforgiving landscapes.