Raspberry Pi - A credit card sized, linux based mini-computer for $30

needing active cooling makes them pretty much useless

some of the new cases have fans built in (but will limit expandability, getting in the way of the pins)

the official word is "continual heavy usage" will cause thermal throttling and a fan will avoid that. also that the 5 is generally cooler than the 4 and faster even if throttling, so it's not as terrible as all that.