A while ago, I read an announcement about BookBoon. It was about quality ebooks on a plethora of different subjects, and as it's our mission to enable a paperless world, pushing the limits of digital document interactivity, I visited the site and I discovered that Bookboon allows you to download quality content in the form of PDF documents.
Moreover these books were offered for free and it's totally legal to download them. How is that possible? How do these guys make money? What is their business model? Is there a business model? Of course, there is! But first let's take a look at the site: