For a truly non-standard, very good Calculus book, I recommend Elementary Calculus: An Infinitesimal Approach, by Jerome Keisler. It's available for free at htt

For a truly non-standard, very good Calculus book, I recommend Elementary Calculus: An Infinitesimal Approach, by Jerome Keisler. It's available for free at https://people.math.wisc.edu/~keisler/calc.html https://people.math.wisc.edu/~keisler/calc.html