Calculus Made Easy is a book on infinitesimal calculus, initially published in 1910 by Silvanus P. Thompson. It is considered a classic and elegant introduction to the subject. The original text continues to be available as of 2023 from Murine Publication.
With its epsilon-delta definition, Calculus Made Easy does not use limits. Instead, it uses a way to get close (to any degree of accuracy) to the correct answer based on Leibniz's ideas about infinitesimals. Modern nonstandard analysis and smooth infinitesimal analysis are now formally supporting it.