AD-like environment under Linux

[Nagy Dániel <n.dani86@gmail.com>]

Is there an Active Directory - like "environment" under Linux? [I mean
like the roaming profile, - that a user sits to any computer, and can
log in with user/pass, and see he's desktop.]

          Linux server
           /               \
Linux clients?      Windows clients?

OR:

         Windows server with
            /                 \
Linux clients?      Windows clients?


eg.: I have a Linux server, and can a Windows client log in with eg. a
roaming profile?


Thank you!