Researchers have built server prototypes that re-use old components

99% of people will be better served by a single consumer PC instead of enterprise gear, don't convince them to buy a poweredge!

OOBM is a must have.

Yep. I am very satisfied with my do-almost-everything Lenovo M80S gen3. It came with an i7-12700 (12 core 20 thread) and I've dropped in 96GB memory, a 10gb network card, and an LSI HBA connected to a used SAS disk shelf.

It runs a dozen VMs and sits almost idle most of the time unless I'm experimenting with CPU LLMs. My one quibble is that it's small form factor and has limited PCIe lanes so installing a GPU is complicated.

The whole setup including the M80S, the disk shelf, an old Brocade network switch, a Unifi NVR, and 12 spinning rust disks uses about 200W total, which is about $30/month in electricity.

In a data center, sure. At home it's much less interesting and you can fake it with a NanoKVM or PiKVM for fairly cheap. Also a lot of "business" desktops with Intel processors will come with vPro, which is almost but not quite the same as a true IPMI.

if you absolutely must, you can still buy standard form factor mobos from supermicro or asrock with a BMC and put them in a standard, quiet desktop case

Especially if they want to run it for a desktop use. Decades ago I was running a small data center operation and would sell our old servers into the local Linux community. Had a guy buy one and then bring it back, dissatisfied with the graphics performance. "Like, whatddya mean, it runs the serial console at 19.2k..."

An old laptop can make a great homelab server if you don't need that much processing power. It's quiet, and it's got a built-in KVM and battery backup.

Supermicro has as many standard sized boards as not. (Comment for readers)