A Magical Society: Ecology and Culture and A Magical Society: Silk Road are part of the most recent Bundle of Holding. 10% of all profits on this one goes to Doctors Without Borders.
If you're not familiar with the Bundle of Holding concept, you basically pay $6.95 to get all three of the gaming books PDFs in the bundle (this one's valued at $62). That's a good deal. However, if you increase your payment past the threshold price (currently just above $18) you get 4 extra world-building books (valued at $48) as well as a so-far-unannounced additional book PDFs.
It's a cool idea and a good way to get a lot of gaming material on the cheap while also supporting a good cause. You should drop by the page and pick it up, or read more about it if you're not familiar with Bundle of Holding.