Active Directory Lightweight Directory Services

Active Directory Lightweight Directory Services (AD LDS) allows administrators to create small versions
of Active Directory that run as non–operating system services. Because AD LDS does not run
as an operating system service, it does not require deployment on a domain controller. Any workstation
or server can host an instance, or multiple instances, of AD LDS. Instead of building a domain
controller so that developers have an Active Directory database to work with, you could create an
instance of AD LDS on their workstations for them to test against. You could also use it as a repository
for data used by a customer-relations management program or an address book directory. If you
need a directory to hold data instead of a database, you may want to consider using AD LDS.


reference : mastering Active directory for windows server 2008