Picked up two mystery boxes today. Was quite far out in my guess as to what was in them, but not unhappy in the end. See what you would expect in these two:

Sort of looks like an early 486 tower doesn't it? In retrospect the CDRom drive was a giveaway that all was not what it seems...

Can you say "generic Pentuim 3"? As it turns out: not.
Inside the ATX miditower:

Asus SP98AGP-X... so the most high-end SiS 5591 board out there - not that that's saying much. SiS' somewhat flawed entry into the "Super" So7 stakes. Was supposed to do 100MHz FSB, but generally wasn't stable over 90MHz and Asus didn't certify CPUs over 66MHz to play it safe... Playing it less safe, there's a modded BIOS for this board for K6Plus CPUs. As I have a few of those I intend to see how that goes. In any event, with a K6-3+-500 known to top 600MHz, CPU won't be the limiting factor.
Current CPU is less ambitious, a K6/266AFR. 32MB RAM and an S3 Stealth 3D 4000 (Virge/GX2) says "low-end Windows 98 system", but one with decent components. Case supports that impression. Unimaginative U-profile thing, but nice rolled edges. Apart from that interesting combo of 56k modem and an ISDN adapter, and a Maxtor 30GB HDD (almost certainly a later upgrade, in 1998/1999 10GB would have been huge).
And the other one?

That's no 486! Instead it's a P166 (non-MMX) on an Epox P55-VX board with 32MB RAM and a Diamond Stealth 3D 2000 (Virge) with 2MB upgradeable to 4MB. Which sort of begs the question why on earth this person chose to upgrade from this P166 (on an MMX/K6-capable board) to a K6/266 with otherwise pretty much identical specs... nice extra: the original CT1740 Sound Blaster 16 in all its noisy (and dusty) glory. Probably that was a holdover from whatever older system was originally built in this case.
One weird thing though:

What on earth is this? All four wires lead to the PSU, so my best guess would be a heath robinson fan controller for the PSU fan, complete with temperature sensor.