I understand that Linux is working for you but Cyberax has a very good point about corporate infrastructure management. Linux is way behind in this area. If you're not aware of what is meant by corporate infrastructure management look at what FreeIPA provides (http://www.freeipa.org/page/About). The whole point of FreeIPA is to take a bunch of tools and provide similar functionality to active directory. AD isn't anything special technology wise. It uses a lot of the same technologies everyone else uses (LDAP, Kerberos, etc...). What AD does well is that it integrates it into a nice easy to use package that makes administration of 10s or 100s of thousands of users easy. Its the tight knit integration of services which makes AD useful and while FreeIPA is gaining ground it still has a way to go. The ability to survey boxes and push out patches and policy though AD is also a big feature. We have similar tools that can do this (CFEngine and Puppet) but once again show me a single package that has all of this integrated and makes it trivial to ensure you're compliant on your network for patch levels?