A group at the Swiss Federal Institute of Technology in Zurich have adapted some quadrocopters (a helicopter with four blades) to juggle a ball back and forth. Multiple robots can keep a ball up in the air by passing it back and forth between each other. Getting a volleyball game out of these robots can't be that far off. Kudos to the team, Mark Müller, Sergei Lupashin and Raffaello D'Andrea.
To quote The Simpsons: I for one welcome our new robot overlords.