Under a Front Range Community College President’s Innovation Grant, I wrote open source textbooks for Calculus 1 and 2, along with my former student Jenna Allen who illustrated them in glorious Asymptote. Since then, fellow FRCC instructors/faculty Joe Darschewski and Aaron Allen have taught from these and subsequently joined in creating the updated versions of these based on classroom feedback! You can view and download them for free here.
These were built using Overleaf, a shared editing editing platform for LaTeX. As they are shared under a Creative Commons license, you are welcome to view the source code and even copy the entire project for your own editing and use. Here are links to the projects: Calculus 1 Textbook Overleaf Project and Calculus 2 Textbook Overleaf Project.
If you like the idea of great quality, free, editable mathematics textbooks, check out some my colleague’s works!
Discrete Mathematics by University of Northern Colorado’s Oscar Levin
College Algebra and Precalculus by Lakeland and Lorain County Community College’s Carl Stitz and Jeff Zeager.