RAA - ruby-ldapserver/0.2

ruby-ldapserver is a lightweight, pure Ruby skeleton for implementing LDAP server applications. It is intended primarily for when you wish to build a gateway from LDAP queries into some other protocol or database; it does not attempt to be a full implementation of the standard LDAP data model itself (although you could build one using this as a frontend)

The Connection class handles incoming connections, decodes ASN1-formatted LDAP requests, and creates an Operation object for each request. The Operation object further parses the ASN1 request and invokes methods which you override to perform useful work. Responses and exceptions are converted back into ASN1 and returned to the client.

Since it's written entirely in Ruby, it benefits from Ruby's threading engine.