Outlook and a LDAP/global address book

Looking to create a centralized address book for around 50-60 users to access and update entries and create distribution lists easliy?
Is there a program that would allow me to create an address book that would be easily updated by users whilst being solely (centralized) universal to all client PC’s, I do not want to use an exchange server and also feel that the address book would benefit from the inclusion of distribution lists. If there is such a program, can anyone tell me what it is and if it is any good. The reason I ask is that I want to look into the possibility of using such a program, before advising whether or not an exchange server is required. I would also appreciate any other comments concerning this as there may be some other valuable and valid ideas concerning this problem and how to resolve it.