It's a fairly typical 1U HP Proliant server, which counts as "enterprise gear". I don't remember the model but it's somewhat unremarkable. It only has like six bays in the front, and I use one for a NixOS install, and two of them with SSDs for read and write cache. It has an old 10 gigabit ethernet card for connectivity. The server I bought used for around $150, the ethernet card I got for about $35 used on ebay.
The actual disks live in 8 bay external chassis, and connected via USB3.0. This may sound horrifying, but USB3 is rated for like 5 gigabits, way more than you can easily get from a home RAID with spinning disks. I have a PCIe 3.0 x16 USB3 card in there, with four plugs, each with a dedicated controller, meaning that in theory each port could get 5 gigabits. The reason I could fairly easily get eight more in there is that I'm only using three of the four ports, so without much effort I could buy 8 more drives (of any size I suppose), put them into another 8 bay chassis, and just add vdev to my RAID. This particular PCIe USB card was $41 on eBay.
I use ZFS for a software RAID.
This sort of happened accidentally; I didn't used to have a rack mount server, I was using a bunch of Nvidia Jetson Nanos, and as such there wasn't a real way directly plug hard drives in, so I ended up having to use the external chassis. Eventually I bought three of those cases, had all the drives in there, and when I decided to buy a "real" server it was substantially easier and cheaper to just add proper USB support to a server than it was to find a decent 24-bay server at a decent price, particularly since I already had the cases.
In hindsight I probably should have got chassis that have eSATA support, but they've been getting decent speed and it's an extremely convenient system. It's also come in handy once when I accidentally broke my server, and I needed to get files off the RAID; all I had to do was plug them into my laptop and mount the ZFS RAID there.
ETA:
Forgot to answer what I use to manage it. I installed NixOS on my server with a pretty vanilla ZFS on Linux install and an NFS mount. I do the tmpfs-on-root trick, so the root partition gets nuked on every reboot. https://elis.nu/blog/2020/05/nixos-tmpfs-as-root/
I don't use any fancy GUI tools or anything; NixOS does a good enough automating away the un-fun parts of maintaining a server, and if I break my server I can very easily roll back to a previous state, and if I really have to, reinstalling it from scratch takes like 20 minutes since I can just copy over my configuration file (which I back up on Gitlab) and have everything automatically set up again. NixOS is pretty cool.
ETAA:
According to `dmidecode` and `lscpu`, server model is `ProLiant DL380 G7`, 24 cores, 128GB of RAM. I think it's actually 12 cores, and it says 24 because of hyperthreading.
It's pretty unremarkable. I like it a lot, but it's a fairly typical and bog-standard used server.