Maybe Calculus Made Easy by S. Thompson (more recently revised by Martin Gardner, but that new edition is under copyright). Maybe Hardy's Course of Pure Mathematics. However...
Modern books use, in some areas and cases, more modern notation and approaches. That's helpful because math is not just knowledge but a language for communicating that knowledge.
If money is an issue[1], either of those Gutenberg texts (re-done with LaTeX), or the OpenStax calculus book are perfectly adequate. There's also no reason you couldn't use an AP Calculus review guide, or Schaum's Outlines, which aren't free but are in the <$25 range. Combined with resources like Youtube math channels, Wikipedia, Mathworld, and Sage and Mathematica (version 12 is freely available for the Raspberry Pi, though it'll be limited by hardware performance), anyone could learn calculus from the most dull and stilted and antiquated-notation calculus books ever written.
Math presented in a slightly obtuse way that doesn't lend itself to instant understanding might actually be better, as it forces the reader to think about the concept more, increasing retention.
Nobody needs Spivak's Calculus. I think it's a bit like the subtle meaning of Frost's Road Less Traveled. Everyone self-rationalizes about how their favorite math book is obviously the best, but in reality most of them probably learned the core of that subject from a different, less elegant book. It's not that it doesn't matter at all; better presentations might avoid an occasional unnecessary struggle over a concept, or lead to faster intuition of a visualization here and there, but it ultimately doesn't matter very much.
However, if you can buy a book (or pirate it) and want a modern digital alternative less like OpenStax or Stewart's, and more like Spivak (which sadly is only available in scans), Velleman's Calculus isn't bad, and you can supplement that with a modern analysis book like Tao, Pugh, or Abbott.
[1] Unless you are flat broke—in which case there's no reason even the most IP-respecting person should feel guilty about raiding libgen for learning material—the cost of a textbook approaches irrelevance when you'll spend 50, 100, or even more hours working through it. The opportunity cost of that time at minimum wage is many times the price of the textbook. What are you trying to accomplish by finding something free? Nobody needs to buy expensive textbooks anymore, but if you're opposed to paying money for textbooks on principle, you might ask yourself why.
Modern books use, in some areas and cases, more modern notation and approaches. That's helpful because math is not just knowledge but a language for communicating that knowledge.
If money is an issue[1], either of those Gutenberg texts (re-done with LaTeX), or the OpenStax calculus book are perfectly adequate. There's also no reason you couldn't use an AP Calculus review guide, or Schaum's Outlines, which aren't free but are in the <$25 range. Combined with resources like Youtube math channels, Wikipedia, Mathworld, and Sage and Mathematica (version 12 is freely available for the Raspberry Pi, though it'll be limited by hardware performance), anyone could learn calculus from the most dull and stilted and antiquated-notation calculus books ever written.
Math presented in a slightly obtuse way that doesn't lend itself to instant understanding might actually be better, as it forces the reader to think about the concept more, increasing retention.
Nobody needs Spivak's Calculus. I think it's a bit like the subtle meaning of Frost's Road Less Traveled. Everyone self-rationalizes about how their favorite math book is obviously the best, but in reality most of them probably learned the core of that subject from a different, less elegant book. It's not that it doesn't matter at all; better presentations might avoid an occasional unnecessary struggle over a concept, or lead to faster intuition of a visualization here and there, but it ultimately doesn't matter very much.
However, if you can buy a book (or pirate it) and want a modern digital alternative less like OpenStax or Stewart's, and more like Spivak (which sadly is only available in scans), Velleman's Calculus isn't bad, and you can supplement that with a modern analysis book like Tao, Pugh, or Abbott.
[1] Unless you are flat broke—in which case there's no reason even the most IP-respecting person should feel guilty about raiding libgen for learning material—the cost of a textbook approaches irrelevance when you'll spend 50, 100, or even more hours working through it. The opportunity cost of that time at minimum wage is many times the price of the textbook. What are you trying to accomplish by finding something free? Nobody needs to buy expensive textbooks anymore, but if you're opposed to paying money for textbooks on principle, you might ask yourself why.