My oldest machine in almost daily use is my P1 133 MHz non-MMX, DOS + w3.11 jukebox machine. The AWE32 in there sounds so much better than any other PC/onboard soundcard i own so i prefer this thing for playing demoscene/tracker music (mod, xm, s3m, etc) and also for listening to various online radio streams (mainly scenesat and quantum radio @TQW BBS).
Aside from various other retro machines i turn on every now and then my main PC is still a socket 775 Core2 Quad (Xeon version, one of the rare ones that just work in that socket).
Most people will probably consider this old and outdated by now...
I built this machine back in 2007 and since then it has received various upgrades, most of them when i got some hardware for free that was better than mine. I used to have a geforce 8800 gts, that one died after 3 years of use, then got a radeon 6850 which i've used until ~2 years ago. That was then replaced by a radeon 6950 i got for free, and shortly after a borrowed a RX 570 from a friend which i still have (and considering the insane hw prices i'll probably cling to the thing for as long as possible 😁)
The hardware is *almost* maxed out, 8 GB DDR2 is all the board can take, and the final upgrade will be a modded socket 771 Xeon but that'll need some fiddling extra microcode into the bios and i'm not willing to do this while i still depend on this machine for daily use.
Also interesting: Originally i used 2x 160GB IDE HDDs from my old PC, in RAID-0 via a PCI RAID card to boot XP (yay for slipping in the driver via floppy). Added a bunch of SATA HDDs over the years, installed some linuxes and a win8.1 on those alongside of that XP, and the latest addition was a NVME SSD that came from an i7 notebook that served for 5 years but died earlier than it had any right to.
Because the original win8.1 was installed in BIOS mode and the BIOS doesn't support NVME *at all*, I had to slap an extra SATA SSD in there that holds Clover (a bootloader from the hackintosh scene that can emulate an EFI on machines that don't have one) and use that with a bunch of extra EFI modules to boot the win8.1 on the NVME SSD (in EFI mode). It's crazy fast considering it was never meant to have that but the hacks required to get this working are kinda nasty.
Basically i just kept adding to the thing and most of the old stuff is still in there. The mainboard has stayed but cpu/gpu/ram changed over time. It's also been in a state of permanent overclock since day 1 so i'm amazed it lasted this long.
So umm... it's all a gigantic mess and there's a ton of OSes on the thing and i've lost track of which disks hold which partitions, etc. Hope that the thing holds on just a little bit longer until the crazy hw prices drop and i can finally get something new and start from a clean slate.
If you've played Factorio, this is basically the essence of Factorio in hardware form.