It's noble of you to only add free books, but I would suggest you might want to reconsider that.
The quality of some commercial books is just so much better than any free book & you'd be able to make some money out of it through providing Amazon affiliate links.
The books posted by OP is actually commercial books though. Books like Mastering Bitcoin, Decentralized Applications, etc that was published by O'Reily and so on. But he provide the PDF file for free.
OP, are you sure this won't be considered like some kind of piracy?