Yet Another Calculus Text: A Short Introduction with Infinitesimals
According to The Orange Grove, "This free textbook is an introduction to calculus based on the hyperreal number system. For example, much of the content deals with infinitesimal and infinite numbers. The text is aimed primarily at readers who already have some familiarity with calculus. Although the book does not explicitly assume any prerequisites beyond basic algebra and trigonometry, in practice familiarity with basic calculus is required. Contents: 1) Derivatives. 2) Integrals. 3) Answers to Exercises."