The Lightweight Directory Access Protocol (LDAP) has been a standard for many years. But since LDAP had its genesis in the old X.400 and X.500 days, LDAP has always been a protocol that invited corporate (rather than community) involvement. Consequently, the most visible LDAP implementations were commercial offerings from infrastructure providers. Commercial providers included: Microsoft (Active Directory), Siemens (DirX), IBM (Notes), Banyan (Vines), Zoomit (Via), and Netscape (Enterprise Directory Server). Some of these products are gone. Many remain.
But the days of commercial LDAP are numbered, I hope. Last year, Red Hat acquired the Netscape directory source code from AOL. It was widely rumored that the product would be released under an open source license. Well, that time has come. Red Hat has released the product under a GPL (with exceptions for certain sub-components). The new product is known as the Fedora Directory Server. While I expect many new implementations to arise, I am personally looking for some great certificate systems to folllow.
All in all, it is amazing to see the march of technology commodization reaching higher and higher levels of the OSI stack!
-CyclingRoo-