The proliferation of new top-level domains (TLDs) has exacerbated a well-known security weakness: Many organizations set up their internal Microsoft authentication systems years ago using domain names in TLDs that didn’t exist at the time. Meaning, they are continuously sending their Windows usernames and passwords to domain names they do not control and which are freely available for anyone to register. Here’s a look at one security researcher’s efforts to map and shrink the size of this insidious problem.
Been using this in my homelab. Pretty great for Linux machines.
If you need to host for a windows network, samba can provide a Windows Server 2008 level AD DC, as well as print and file servers.
You could always install bare LDAP and Kerberos, but then again you could also try eating a cinderblock.
There are alternatives, but they all have their usecases and compromises in comparison. Most businesses want a cookiecutter one size fits all solution. AD is the closest thing.