Is there any solid open source solution to replace Active Directory?

YES I've tried to set up LDAP but I can't get it to work. I've tried to follow multiple guides but nothing seems to work. I don't mind putting in the effort, but I'm really put off with how hard this is. I guess I need a complete guide from setting up the servers, to adding the linux desktops to the domain...

Anybody know of any guides like this?

EDIT: I should have been more clear. I'm trying to make a pure Linux domain and I want to do central authentication, roaming profiles, etc using software built for Linux. No Windows computers will be used in this environment. Sorry for the confusion.