I'm not sure what else you want from a directory server but a "distributed user authentication store." Maybe you're referring to file and print services? Email

I'm not sure what else you want from a directory server but a "distributed user authentication store." Maybe you're referring to file and print services? Email server integration? All of these kinds of things should be available, regardless of what platform the directory server is running on. I'd make some long argument about the Linux market longing for an easy-to-use directory server, but I see that Novell Directory Services still lives on as NetIQ, and I've never heard of anyone using it, so maybe the market just isn't there. (Another victim of Microsoft's monopoly.) So maybe it doesn't matter that AD isn't platform independent. I guess companies running a lot of Linux are happy to hassle with the nightmare that is OpenLDAP.