Relative delivered a custom-built desktop PC that they no longer want. Inside it is the dustiest computer I have seen in decades, with brown dust caked and clogging the vents. I am amazed that all the fans still work. I drained the battery on my handheld blower, and I still have a ways to go. I suspect this was assembled about fifteen years ago (processor is an i3-2100), put into use, and then the case was never opened again.
Boots perfectly. Fans are whisper quiet. Mechanical hard drive spun up fine and passed all checks. It may be a little old, but my relative did a nice job putting this all together.
I'm going to see about swapping in an SSD, then checking how usable it is (current operating system, videos etc.). If it's good, I'll try and pass it to someone in the neighborhood.
Huh. No WiFi. Was not expecting that. I think I actually do have a PCI-E WiFi/Bluetooth card in a box somewhere around here ...
For now, I'm close enough to the router that I can run a length of Ethernet cable, but that's not going to fly with most people.

I've booted LMDE 7 off of a USB stick, found an Ethernet cable, found the spare trackball (Logitech M575S - great design in every way except that the buttons are terribly mushy), and ...

It can play a The Wide World of Jank (thank you, @BigBadBiologist) at 720p and 60 fps. Does so at 20% processor load, which doesn't seem terrible.

That's promising enough that I can continue with this one. I'll find the wireless card, replace the mechanical drive with an SSD, and find it a home.

@GamesMissed what other use would anyone ever need for a computer? ❤️