New test version of Samba is available for download. You can check their Release Notes. They’ve spent 3 years in development. It’s still a Technology Preview to allow users, managers and developers to see the progress and get the feedback and support. This means it’s still not a Stable release and they’ve warned that Technology Preview is not secure.
New features of Samba 4:
Active Directory support
Built in LDAP Server
Integration of user-friendly SWAT
New VFS (Virtual File System) features
New java script interface that can talk to samba internals
Based on LDAP-like Database