Raspberry Pi servers are the low-cost machines in the data centre. Broadbent Host builds a Pi 4 or Pi 5 to the brief and houses it on a 1 Gb/s uplink, or you co-locate a Pi you already own.
The usual operating system is Raspberry Pi OS. The server can be managed or self-managed, and a domain can be added. NVMe storage and a Pi HAT are options on the product page.