Dr Anders Lyhne Christensen, from BioMachines Lab of the Institute of Telecommunications in Portugal has developed a swarm of aquatic robots and they are all powered by Raspberry Pis. They communicate with each other over an adhoc wireless network. The boats themselves have CNC-milled foam hulls with some 3D-printed elements. It is an extraordinary project and you can find a lot more about the methods and computational elements used by watching the video below or by visiting the BioMachines Lab website. The code for the robots is all available on GitHub.