Active Directory is just a fancy name for LDAP, Kerberos, and DNS (often in combination with CIFS). There's no reason why you cannot use an equiv in a partly or pure Linux/UNIX environment. And indeed, there are many partly Linux/UNIX environments where the servers are running on Linux/UNIX yet the clients are running on Windows. The killer feature of Windows is that people are used to running it as desktop, meaning a less steep learning curve. Another one to add to the list of features is Exchange, but even that has *NIX alternatives.

> Active Directory is just a fancy name for LDAP, Kerberos, and DNS (often in combination with CIFS).

I don't quite agree, Active Directory is an easy to learn and deploy implementation of LDAP, Kerberos, and DNS (often in combination with CIFS) with a friendly GUI interface. It also adds Group Policy, which is less simple to replicate on Linux. Then it adds a huge pool of admins which have been through the vendor supplied training process. I can show people how to create a user and add them to my company defaults in minutes, and not just because they are familiar with Windows, but because they are familiar with the desktop metaphor

I am a keen Linux user, I am typing this on Linux in fact. We have lots of processes running on Linux in fact. But I cannot replace the ease of AD in Linux. And more than that, our ERP client only runs on Windows...

I've found that FreeIPA tends to be a fantastic replacement: https://www.freeipa.org/

If you're using Red Hat/Fedora GNOME desktops, you can pair that with Fleet Commander to set up desktop policy: https://fleet-commander.org/

At some point soon, I expect it to work for SUSE and Mageia systems, too.

I currently run this on a Fedora Server setup to pair with some Fedora Workstations I manage.

Except AD lets you do an awful lot more than this with Group Policy - you can configure and enforce endless amounts of settings on client machines from the simple - wallpaper for example - to software installs to executable restrictions...

This is a big plus for locking down mostly untrusted users (eg average employees in a larger enterprise).

Edited to fix stupid autocorrect.

Group Policy (which is really a mostly-unrelated thing propagated through AD) is probably the hardest-to-replace part of the equation.