I have mini-ITX board in a mini case. 4 bays, 16 GB RAM of DDR3-L and a slow but very low TDP CPU. This thing is very low power but it’s on 24/7.

Runs home assistant with zigbee, rtl433 and whatever it detects over the network. A few older game servers (minecraft, minetest/luanti, quake 2), miniDLNA, … Arch Linux, so rolling release and always up to date with the latest versions.

Served me greatly and I haven’t upgraded because it still does what I want and I can’t find any modern CPU with a TDP this low.