Probably stuff it to the brim with virtual machines, that kind of usage
https://www.ahead-it.eu/en/shop/servers/embedded-iot/intel-a...
Those?
Technically they are fanless but I wonder how well they would work outside of a rack with high ambient, they seem to be fanless themselves but still rely on having plenty of air pulled across the casing. Mounting them vertically might work. 850 euro though!