When Microsoft delivered Windows 8.1to manufacturers, some developers were more annoyed than overjoyed -- unlike in years past, they weren't getting advance copies to help optimize their apps. The company has heard their complaints, however, and it's now offering the Release To Manufacturing builds of Windows 8.1, 8.1 Professional and Windows Server 2012 R2 to both MSDN and TechNet members. The enterprise edition of Windows 8.1 will be available later in September, Microsoft says. Regular users will still have to wait until the mid-October launch to get their turn, but the early developer release should lead to a healthier stock of Windows 8.1-ready apps in the weeks ahead. Update: In case you'd forgotten, 8.1 also arrives with a "fully built-in Skype app." TheSkype blog details new features like the ability to answer calls from the lock screen, a window that automatically adjusts when you open up links and click to call from Internet Explorer.