A system for running distributed code over multiple PI Picos connected to each other. The reference implementation has them all standing on end in a ring, resembling a Cray supercomputer.
Wire all of the picos in parallel connecting GPIO 10,11,12,13 and GND to all of the picos. Each pico needs powering separatly either from the USB bus or 3v3 pin. Make the I2C bus as short as possible and you will need one pair of 4k7 Ohm resistors to +3v3 on GPIO 10 and 11, ideally in the last processor in the chain.
The Code is the same for all Picos, to specify a controller add a wire from GPIO 22 to GND There must be (only) one controller in each cluster.