Wheels are great for moving fast and efficiently, but bad for negotiating terrain. Legs are great for negotiating terrain, but not as good for moving fast and efficiently. To create a robot that can move fast when it needs to but can also adapt to get around complex surfaces, a group from National Taiwan University's Bio-Inspired Robotic Laboratory (BioRoLa) created Quattroped, a robot that can turn its wheels into legs:
How awesome is that, right?! It would probably be most accurate to say that the bot's wheels transform into not legs but whegs, several varieties of which we've seen over the last couple years. Whegs function similarly to legs, except that they move in a circle instead of back and forth, making them more effective at clambering over obstacles. And as you can see in the video, the bot can even "walk" by moving alternate pairs of whegs.
Quattroped is equipped with GPS, a vision system, and laser ranger, and the team is actively working to integrate more sensors to improve the perceptual capabilities of the robot. On the software side, it's running National Instruments' LabView, and while a remote PC is involved for control and data logging, most of the processing is done on the robot itself.
This is an amazingly adaptable platform, and besides the additional complexity in the wheel hubs and some minimal compromises on wheel strength, this type of thing seems like an obvious way to give mobile robots significant additional capabilities.