Windows 8.1: Free ebook

http://blogs.msdn.com/b/microsoft_press/archive/2013/10/14/free-ebook-introducing-windows-8-1-for-it-professionals.aspx

These books are usually VERY good.  I have read a number of them in the past and they provide a good depths of knowledge while covering the new features.  It is a great way to get to know the newest tech.  If this  is up your alley here are a few other links to check out:

CanITPro is one of the premier sites to learn about Microsoft technologies and they recently posted a series of free books as well – http://blogs.technet.com/b/canitpro/archive/2012/08/08/22-free-microsoft-ebooks-to-add-to-your-must-read-list.aspx

Here is a third option for free books.  It is a HUGE list of the available free Microsoft books – http://blogs.msdn.com/b/mssmallbiz/archive/2012/07/27/large-collection-of-free-microsoft-ebooks-for-you-including-sharepoint-visual-studio-windows-phone-windows-8-office-365-office-2010-sql-server-2012-azure-and-more.aspx