In 2017 a friend on IRC sent me a piece of kit they didn't need any more - a PC Engines apu1c4. I ran pfSense on it for a while, then FreeBSD, and about a week later I switched to Alpine Linux. This is a collection of information about this unit, for my own reference, but I hope it's useful to someone else.
The apu1c4 is a 1GHz, dual core amd64 appliance with 4GB of DDR3 RAM. It's outdated by several revisions now. It lacks a physical (video) console, instead using a serial console over DB9 RS232. It has support for SATA and miniPCIE SSDs, but I'm currently using an SD card for the OS, which is presently FreeBSD.