Zoho Directory (ZD™) is a centralized admin console for easy management of all services in our organization. The prime feature of Zoho Directory is the unification of user management (i.e) all features including adding a user, admin operations for the org, etc... can be done through a single admin console.
Active Directory (AD) by Microsoft is centralized and standardized system that automates network management of user data, security and distributed resources. In simpler words, it allows management and storage of information and provides authentication and authorization mechanisms. i.e. You can store information of your organization members, include their devices, verify credentials and define their access rights.
Lightweight Directory Access Protocol (LDAP) is an open, vendor-neutral, client/server application protocol used to access and manage directory information. It is organized in a tree like structure called Directory Information Tree. A few of popular LDAP servers are: OpenLDAP, ApacheDS, OpenDJ, 389 Directory Server.
Zoho Directory Sync Tool performs a one-way synchronization from your existing LDAP server to the Zoho Directory Admin Panel. This enables you to maintain all your user identities in a single place, without having to add, edit, or disable user accounts manually in the Admin Panel.