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I am working on creating a cluster computer using three Raspberry Pis. Once I get that working, I might see what I can do with the smaller model, the Raspberry Pi Zero. If I did, this interface would be a good start. It sits on top of a regular Pi and connects up to four Pi Zeros to it.
Pimoroni. Cluster Hat 2.0. Available at https://shop.pimoroni.com/products/cluster-hat.