When I listened to Dr Michael Brown interview Dr Craig Keener, one of Keener's books came up. Its a background commentary that gives historical context to the New Testament. I decided to see if I could find a digital version and there is one! It can be integrated with the Olive Tree Software platforms. I use Olive Tree on my Android devices so I was excited.
IVP Bible Background Commentary: New Testament, The by Craig Keener... for iPhone, iPad, and Android - Olive Tree Bible Software
As a bonus I found out that there is an Old Testament version! It's available as an e-book!
The IVP Bible Background Commentary: Old Testament (eBook, Exclusive)