Servers / infrastructure
Directory / SSO Services
This field has seen rapid changes for macOS admins in the last years - with SSO-service providers like Okta gaining market relevance rapidly, and new tools like noMAD chaining this to macOS topics, like Kerberos tickets, 802.1x, and directory services. The reason why this gained relevance: classical Active Directory Binding increasingly got too inflexible to work properly, with the majority of the clients being mobile now. Right now, AD still has a big relevance for managing access rights, structuring companies’ departments in OUs and this will probably remain so for Windows based companies - not necessarily for Mac / mixed companies though.
Exchange gained market share recently compared to the main competitor, Google's G-Suite; probably due to the fact, you can run it both on premise and in the cloud (now that the Cloud-capabilities of the G-Suite are no longer an obvious advantage over Microsoft’s Azure). Also, Microsoft is more trusted than Google, in regard to data security and Exchange integrates very well with Active Directory, and some other Microsoft services like SharePoint (although this is mostly true for Azure-based Exchange; integrating on premise Exchange-installations with Cloud-based MS services is not always possible, or easy).
For Mac admins, it esp. regained relevance with the release of Office 2016 - Outlook for Mac was completely rewritten on that occasion, and since then it's grown even much better, now being a very serious alternative to Apple Mail. Especially, when combined with Exchange: since many years, Mail.app still doesn't support important MS Exchange features like Public Folders, used in order to share calendars, address books etc. - just as an example.
File servers & shares
As mentioned under NAS, this type of storage has gained a huge relevance over the last years - all the same, Windows server systems still have some advantages, especially if big part of the infrastructure of a company is MS-based. Terminal server, Hyper-V, the possibility to manage ACLs at wish, also locally, etc. - it comes at an according price tag though, similarly to VMWare ESXi, so usually one encounters a mix of various on premises and cloud platforms for file sharing and backups purposes.
Linux / Cloud systems
AWS and Azure have become very dominant in the last years, since services usually need to be available on mobile devices, in micro-offices without secured, well-cooled server rooms, or in co-working spaces. In itself the storage usually isn’t cheaper, also the necessary internet bandwidth is a relevant cost factor (esp. for larger offices); but the cost is rather predictable and planning, deployment of software / services is much more time efficient. Especially in companies with internal software development, and the possibility to deploy virtual machines using orchestration tools like Ansible, cloud environments are almost always more efficient and on premises storage, if at all, used for backups.
My favorite distro is Centos; and scripting is usually done in Bash. See also under Virtualization.