A list server is an application for managing subscriptions to (e-)mailing lists via e-mailed "commands". Active Subscriber is a list server designed specifically to work with Exchange Server 2007 and Exchange Server 2010. Our older product, Ikakura, was designed to work with older versions of Microsoft Exchange.
Yes. If a subscriber does not exist in Active Directory, Active Subscriber creates a new contact in Active Directory and stores it in the same organizational unit (OU) as the mailing lists.
N.B. Active Subscriber also deletes subscribers from the OU if it finds they are no longer members of any lists (or if it receives a non-delivery report), but it never creates or deletes contacts outside the Active Subscriber Data OU - it only modifies those contacts that it "owns".
Ikakura depends on two Exchange services:
1. Microsoft Exchange Active Directory Topology Service
2. Microsoft Exchange Service Host
These should both be on an Exchange Server which is providing Mailbox and/or Client Access roles.