macOS Server
Is the "macOS Server App" available for macs running Snow Leopard. (By buying a current version then signing in with your Apple ID on the computer you want to install the software on)
Question marked as
OS X Server for Snow Leopard only ever came on installable media (DVD etc) and was never an App Store download. You'll either have to contact someone at your local Apple store and enquire there or start looking on eBay etc. I doubt it will even install let alone run on hardware newer than 2009.
https://en.wikipedia.org/wiki/MacOS_Server#Mac_OS_X_Server_10.6_(Snow_Leopard_Server)