Corporate directories, also referred to as “electronic directories”, are a specialised type of database designed to contain hierarchically arranged information on a company’s organisation.
Most of the time, the data pertain to people (users) and/or resources (printers and the like).  But the use of corporate directories is not limited to text searches; they can also be used as address books, for user authentication, to define the company’s security policy and more.
There is a standard used in most corporate directors to perform queries (LDAP protocol).
In the open source universe, OpenLDAP has the best reputation, even if tools like 389 Directory Server also boast a strong functional scope.

Solution	Views	Global Rating
		3.9 5
		4.3 5
Apache Directory		No rating
OpenDS		3.2 5