Wobblegong

Ok, ok, I know "free calculus textbook" is on par with "free unseasoned boiled Brussels sprouts" in terms of crowd appeal, but hear me out. Calculus Made Easy is a 1910 book by one Silvanus P. Thompson, available on Project Gutenberg as a PDF [LINK] or as its own standalone website [LINK]. The very short prologue opens with:

"Considering how many fools can calculate, it is surprising that it should be thought either a difficult or a tedious task for any other fool to learn how to master the same tricks.

Some calculus-tricks are quite easy. Some are enormously difficult. The fools who write the textbooks of advanced mathematics — and they are mostly clever fools — seldom take the trouble to show you how easy the easy calculations are. On the contrary, they seem to desire to impress you with their tremendous cleverness by going about it in the most difficult way.

Being myself a remarkably stupid fellow, I have had to unteach myself the difficulties, and now beg to present to my fellow fools the parts that are not hard. Master these thoroughly, and the rest will follow. What one fool can do, another can."

That's the preface. The first chapter is titled "To Deliver You From The Preliminary Terrors."

It keeps going like this.

So if you know calculus, or don't know calculus, or are just a sassy little fishbirdthing who is delighted by this guy's voice, grab the free PDF or visit the free website. I'm not sure there's a downside to reading this.