In the academic year 2014-2015 I was one of five faculty at Brooklyn College who participated in the CUNY OER program. It was a pilot program back then and has been flourishing ever since.
I wrote an open-source Calculus I book. Calculus textbooks are expensive and my goal in writing a free book is to help students read and learn Calculus on their own. At present students find it hard to read math textbooks because they are written for instructors. This book connects Calculus to art, and it is about as close to "light reading" as a calculus textbook can get. I definitely enjoyed writing it.
S. R. Kingan (2015) Calculus for Everyone, Open Education Resources, 2015.
This book has been downloaded nearly 2000 times and that is not counting my students. Who would've thought it would be so popular! I suppose there is always room for another calculus book.