RTM, Release to Manufacturing, indicates the code is now signed off and available for mass production for mass distribution, that just happened to Windows Server 2008 R2, as it happened to Windows 7, both today. Some of the new features available at this release has been highlighted at Windows Server 2008 team’s blog.
Windows Server 2008 is the most recent release of Microsoft Windows' server line of operating systems. Released to manufacturing on February 4, 2008 and officially released on February 27, 2008, it is the successor to Windows Server 2003, released nearly five years earlier. Like Windows Vista, Windows Server 2008 is built on Windows NT 6.0.