Hi!
This seems to be a minor sensation on GitHub at the moment:
Free Programming Books
Most of these would fall into “other”, I suppose, though there are some bits germane to certain libraries, e.g. databases, web programming, etc.
I’ve read a tiny few of these (a few more have sat unread on one hard drive or another, sometimes for years, mea maxima culpa). For anybody unfortunate enough to think and learn like me, there are a few in particular I’d recommend for honing your Lua (or even general programming) skills:
“Structure and Interpretation of Computer Programs” (aka SICP), for getting a feel for the power of closures, and perhaps some insight into coroutines (which are essentially one-shot continuations).
Paul Graham’s “On Lisp”, ditto, but more for the coroutine aspect from what I recall–in particular, I personally got a lot out of a couple later chapters. (In hard copy, I also own and have enjoyed his “Common Lisp” for much the same reasons, along with Kiczales’s “The Art of the Metaobject Protocol” for further reading on the CLOS class system. Unfortunately I don’t know of free versions there.)
“Learn you a Haskell”, for functional programming generally, and an entertaining read in its own right.
(The languages used in these books are Scheme, Common Lisp, and Haskell respectively, but they’re honestly not as scary as they might look!
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Also, while probably even less relevant, apart from whatever lessons you can draw from the large development post-mortems on Quake (and a little on Doom and Quake 2), Michael Abrash’s “Graphics Programming Black Book” is excellent. A pleasant read and full of wisdom from quite an amazing developer.