What are you looking for your server to do? For just under $20 you can get Apples server app, which gives you DNS, DHCP, mail, print, ftp, vpn, file, netinstall, netboot, network user accounts, and more (not that you can run all services concurrently on a laptop - ram and cpu resources come into play.)
There are 3rd-party and open source applications that will give you some of these functions, often with more granular or more refined control.
The interesting (to me) thing about macOS is that it is Unix. There isn't a "client" version and a "server" version of Unix. There is simply Unix, with all of the server functions built right in. Although this is true with macOS, Apple has removed some of the server functions - or at least removed the graphical user interface for some of the server functions. The server app returns these.