This is one of those, I believe -- Eric Ligman is Microsoft Senior Sales Excellence Manager (whatever that is) and he apparently posts large lists of free Microsoft-stack-related eBooks on his blog at MSDN, such as this list from a few weeks ago (which I think was mentioned on HN back then):
http://blogs.msdn.com/b/mssmallbiz/archive/2015/07/07/i-m-gi...
As far as your needs are concerned, while there are no ebooks about programming languages in this list (aside from PowerShell), there's a bunch about SQL Server in the second half of the list and perhaps other things of interest as well.