Preface Supplementary material and references
These course notes for MATH 215 were written with the help of various other notes, including the following main references. Those references may also be very helpful as supplementary material.
CLP4, the Calculus IV open textbook from UBC. Focuses on vector calculus, but takes a traditional approach, relegating differential forms to the optional Section 4.7.
Lecture notes on differential forms and vector calculus by Donu Arapura from Purdue University. A fairly short introduction to the topic of vector calculus using differential forms.
Lecture notes by George Peschke from the University of Alberta, available on eClass. Approaches the topic in a fairly similar way to these course notes, but with more rigor and generality.
APEX Calculus (version with videos from Sean Fitzpatrick, University of Lethbridge). Open calculus textbook with videos by Sean Fitzpatrick from the University of Lethbridge. Chapter 15 is about vector calculus, taking a traditional approach (without even mentioning differential forms).
Multivariable Calculus, by James Stewart, Daniel Clegg, and Saleem Watson (unfortunately not open nor free). Chapter 16 is about vector calculus, following a traditional approach without mention of differential forms.