Free Learning Programming resources to start hacking on a budget
Just came across this Free-as-in-freedom collection of Programming Languages resources (books, guides, etc) in the form of a Github Awesome list, of which most if not all are freely available on the internet.
I wouldn't exactly call some of them "books" as per quality and quantity, but most are very concise guides, or cover specific aspects of programming that physical books tend to oversee, like Graphics Toolkits or platform specific stuff.
Oh, and this is not limited to programming either, though, just browse the parent repository and have a look yourself (you're welcome). I know I will.