Newest is a HP EliteDesk 800 G2 Mini, i7-6700T, 32GB RAM, 1TB M.2 SSD. I had the SSD, the machine was ~$100US on eBay, and came with 1 stick of 16GB RAM so a matching second was only ~$24. I think right now I could pick up the same for about $200 including the SSD. It runs Proxmox with a few VMs for Minecraft, dev work, a Windows desktop, etc. Really a pretty capable machine for light-ish duty. I can barely hear the fan most of the time and just 35W TDP.
Older is a Gigabyte Brix with a Celeron J4105, 8GB RAM, and an M.2 SATA SSD. It's primarily been my Plex server but hosts a couple Docker containers and a website. It has four external USB3 hard drives. They're getting pretty old but I sometimes see them pop up in usable configs for ~$100 on eBay. I normally never hear the fan (the hard drives are louder) and just 10W TDP.
I'm really considering getting another ultra small form factor like that HP, but with the 7th gen i7 so it has hardware support for encoding HEVC / H265.
I've also had an old i3 Thinkpad running until recently. Also nearly silent and bonus that it has it's own battery and display/keyboard when I need to debug something.