As part of DARPA’s Ground X-Vehicle Technologies program (GXV-T), a team from Carnegie Mellon University National Robotics Engineering Center created a hybrid wheel-track which can configure between a traditional round wheel and a triangular, tank-like track in seconds. The intent behind this design is to allow optimal mobility between hard and soft terrain as required, while still inside the same vehicle.
The Ground X-Vehicle Technologies program itself was launched to find ways to “improve mobility, survivability, safety, and effectiveness of future combat vehicles without piling on armor.”
You can read more about the GXV-T demonstration here.