It's a download, which isn't so unusual, although most of the books that are free to download are in the public domain.
Little Brother was only published in 2008 but the author Cory Doctorow makes it freely available online
here.
He says it makes good commercial sense and it does. I read some of it online and liked it enough to want to buy the hard copy so I could read in bed and on the sofa. It's also in line with his philosophy, which is don't punish "pirates", don't even have such a concept as "pirating", make information more freely available not less. The enemy of book sales isn't downloads, it's obscurity. That makes sense to me.
The book is Young Adult and it's about what happens in the wake of a terrorist attack on San Francisco. The main theme is how the government responds to terrorism by putting in place systems that only harm the innocent. I believe that this is true. In Britain, you can't be held in prison without due process of law - unless you're suspected of terrorism.
I found the book to be a fun read but then I like near-future science fiction, computers and teenagers. Neil Gaiman says
I'd recommend Little Brother over pretty much any book I've read this year.
I don't often recommend books but this one is worth a look and it needn't cost you anything at all.