Updated on 27 October 2015
IMPORTANT: AAD Connect has replaced AADSync and DirSync. Reference: Azure Active Directory Sync
Reference(s):
- Integrating your on-premises identities with Azure Active Directory
- Microsoft Azure Active Directory Connect (Download)
- Azure AD Connect: Version Release History
- Search “azure active directory connect requirements”
- Integrating your on-premises identities with Azure Active Directory
- Prerequisites for Azure AD Connect
ODDYTEE 
Added references on 27 Oct 2015…
– Search “azure active directory connect requirements”
– Integrating your on-premises identities with Azure Active Directory
– Prerequisites for Azure AD Connect