The Raspberry Pi 4 is pretty powerful by single-board computer (SBC) standards, but what if you could combine up to four of them into one super SBC? Well, IPTerra seems to think that is a good idea and has created the CloverPI for that purpose. Theoretically, the CloverPI is compatible with any SBC that has a 40-pin GPIO.
https://www.notebookcheck.net/CloverPI-Combine-four-Raspberry-Pi-boards-into-one-powerful-cluster-device.456003.0.html
How can it be a "super SBC" when it's made of six boards? Do you understand the meaning of Single Board Computer? Perhaps an SBC cluster might be a better name for it.
Frankly, I find it silly. Those Ethernet connections are a proper mess. I would rather use a standalone switch. You can use standoffs to stack the boards (or use a "dog bone stack", etc.). That just leaves a clean solution for powering the things.