Open Educational Resources (OER)

OpenStax
Introductory Statistics

From the Summary:
"Introductory Statistics follows scope and sequence requirements of a one-semester introduction to statistics course and is geared toward students majoring in fields other than math or engineering. The text assumes some knowledge of intermediate algebra and focuses on statistics application over theory. Introductory Statistics includes innovative practical applications that make the text relevant and accessible, as well as collaborative exercises, technology integration problems, and statistics labs. "

Community Calculus

From the MAA review of this book:
"The discussions and explanations are succinct and to the point, in a way that pleases mathematicians who don’t like calculus books to go on and on.
The book covers the standard material in a calculus course for science and engineering. The size of the book is such that an instructor does not have to skip sections in order to fit the material into the typical course schedule. The single variable material is contained in eleven chapters beginning with analytic geometry and ending with sequences and series. The multivariable material consists of five chapters and includes with the vector calculus of in two and three dimensions through the divergence theorem. The book ends with a final chapter on differential equations.
There are sufficiently many exercises at the end of each sections, but not as many as the much bigger commercial texts. Also available are WeBWorK problem sets keyed to the sections of the text. Some students and instructors may want to use something like a Schaum’s outline for additional problems. "

Calculus

From the Text:
"This is the free digital calculus text by David R. Guichard and others. It was submitted to the Free Digital Textbook Initiative in California and will remain unchanged for at least two years.
The book is in use at Whitman College and is occasionally updated to correcterrors and add new material. The latest versions may be found by going to http://www.whitman.edu/mathematics/california_calculus/"

Geometry with an Introduction to Cosmic Topology

From the Text:
"Motivated by questions in cosmology, the open-content text Geometry with an Introduction to Cosmic Topology uses Mobius transformations to develop hyperbolic, elliptic, and Euclidean geometry - three possibilities for the global geometry of the universe.
The text, written for students who have taken vector calculus, also explores the interplay between the shape of a space and the type of geometry it admits. Geometry is suitable for a semester course in non-Euclidean geometry or as a guide to independent study, with over 200 exercises and several essays on topics including the history of geometry, parallax and curvature, and research aimed at determining the shape of the universe. More about the text can be found in the Preface.
Previously published in 2009, the author has made this updated and revised 2018 Edition freely available, thanks in large part to the PreTeXt Project.
Read the MAA Review"

An Introduction to Combinatorics and Graph Theory

From the Text:
"Combinatorics is often described briefly as being about counting, and indeed counting is a large part of combinatorics. As the name suggests, however, it is broader than this: it is about combining things. Questions that arise include counting problems: “How many ways can these elements be combined?” But there are other questions, such as whether a certain combination is possible, or what combination is the “best” in some sense. We will see all of these, though counting plays a particularly large role."

Introduction to Probability

From the American Institute of Mathematics:
"This book of about 500 pages has become a classic because of its engaging style, interesting examples, historical notes, pedagogical use of computer simulations, and more than 600 exercises. Thanks to the American Mathematical Society the book is freely available...[the ]text [is] for a first course in probability assuming some understanding of calculus [and] is open source and can be freely distributed and printed."