Packt is doing a promotional deal and giving people the chance to get a free ebook from their catalog.
Now - 2 things you should know. Apparently the promotion has been successful in terms of generating interest as the site seems to be dog slow and at times just errors out. Second, the quality of their books is uneven at best. So you may not feel that free is even low enough a price on some of their titles. I'm not endorsing all their books, though some I've read were o.k. It's free - so you can't complain too much.