[TheNewsIsHere]

It had a five year run and saw four different hardware models. It included two hard drives instead of either one hard drive and an optical drive, or just one hard drive (after they ditched ODDs).

Mac OS X Server was its own operating system originally. It was still the same core OS, but had a ton of additional servers built in. Non-exhaustively, they included IPSec VPN, email, calendaring, wiki, SMB and AFS file shares (including support to act as a Time Machine backup destination), LDAP, DNS, and software update caching before it came to macOS proper. The Server app released via the App Store was a shadow of Mac OS X Server.

These were quite popular in small professional offices like law firms.

[astrodust]

I saw it save the ass of a client who had one, as they got robbed and all their desktop computers, mostly iMacs, were stolen. The Mini was as much as lost in the wiring in the network closet and was overlooked, so everything had backups.