OpenDS, the 100% Java implementation of an LDAP v3 directory has reached the 0.9 milestone earlier this week. At this point, it is an LDAP v3 compliant directory with multi-master replication and access controls just to name the main features. Next stops are the beta release and a 1.0 version later this year. In the mean time a Summer 2007 Bugfest has just started with prizes for people helping fix as many as 130 defects listed today.
OpenDS comes with a Java Web Start installer and data to populate the directory. It really doesn't get any easier than that to start using an LDAP directory. If you need to speak XML to OpenDS rather than LDAP, the DSML gateway (implemented as a WAR archive) is also available.