Server was never as widely used as the consumer versions of macOS, but macOS Server has a long history going all the way back to Apple’s late-’90s acquisition of NeXT and its NeXTSTEP software. NeXTSTEP was adapted into a project called “Rhapsody,” which added support for some longtime Apple software and a more Mac-like user interface and was initially released as Mac OS X Server 1.0 in March of 1999. This initial version of Mac OS X Server shared a lot of underpinnings with what would become Mac OS X but predated important user interface elements like the Dock and the Aqua theme, which would launch two years later in the first consumer version of Mac OS X.
I have found memories of running Mac Server for all sorts of things from file hosting, vpn, media server, and all around digital hub. At one point running on a Mac mini connected to my TV over hdmi and able to ssh into from anywhere in the world.