Apple delivered iOS 8 to the developer world at WWDC in June 2014, before launching it at the wider world in September of the same year. The iOS 8 SDK was somewhat over-shadowed by the simultaneous announcement of a new programming language in the form of Swift, however this didn't mean that the core OS had been overlooked at all. Quite the opposite - a huge number of new APIs had been introduced, powering tons of new functionality.
iOS8: Day-by-Day is a review of the most important of these. Busy developers don't have time to trawl the WWDC videos and Apple documentation. Instead they'd like to get a high-level summary of the new possibilities, alongside some working sample code. This is exactly what iOS8: Day-by-Day provides. It started out as a blog series, and these blog posts now form the basis of the book.
You can see the original blog series at shinobicontrols.com/iOS8DayByDay and all the source code is available on GitHub at github.com/ShinobiControls/ios8-day-by-day