Using OS X Server resources on non-Macs
Server data app on OS X is highly standards compliant. LDAP is industry-standard (but it's not active directory),  Mail is IMAP, CardDAV, WebDAV and CalDAV. All are quite standard and ubiquitous.  Filesharing uses SMB3. 

Unless you have highly specific/rigid client requirements or are wedded to certain client apps, you should be able to make productive use of server.app services across multiple client operating systems.