http://www.zytrax.com/books/ldap/
"Once upon a time OpenLDAP was the only game in the Open Source town. It is still regarded as the LDAP reference implementation and remains an excellent system with many production implementations and actively developed. It is, however, no longer the only game in town. The ApacheDS (Apache Directory Server) project has reached a state of maturity which means it must now be taken seriously. Written in Java and with an embedded database-engine, TLS and fully LDAPv3 compliant and with some interesting ideas it is available natively on a wide range of platforms. All future versions of this guide will progessively introduce material describing the use of ApacheDS while continuing to document OpenLDAP." The site is also popular for its DNS guide (which has been published as a book also): http://www.zytrax.com/books/dns/ -- Ersin Er
