It's a PDF file that outlines the history around some of Michael's unreleased songs. It isn't entirely meant to provide entirely new information (though I'm hoping it does for some of you) as much as correct any misunderstandings that the fan base may have. People still incorrectly associate songs to incorrect albums or timelines - I'm hoping to stop that as much as I possibly can.
It also corrects which rumored titles are real and which aren't. It doesn't touch on every song - just those with a lengthy, readily available back story that some people may not be aware of.
As Zakk said, compiling every song the estate has in their possession is impossible without their full cooperation, which I do not have. You'll only be seeing titles that have been making the rounds for ages. But hey, who knows? Maybe some people will learn a few things.