The InJoin Directory Server X.500/LDAP directory server with support of SSL/TLS, SASL and X.509 authentication. There are several other directory-related tools from CriticalPath available

An industry's leading solution for large-scale, business-critical directory service applications.

This is the source distribution of the latest free ISODE release patched for working with Linux. This contains the implementation of many OSI protocols over TCP/IP and QUIPU X.500 directory server.

Provides a robust, scalable and trusted LDAP/X.500 directory service, incorporating specific security and management functionality.

High Performance X.500/LDAP directory server build on top of an OO database and a WWW based management interface.

They enable companies to build a standards-based, distributed directory that offers a common storage space for data regarding people and resources.

Several X.500 products available from Brunel University,including Wlu, a web gateway to X.500.