I am teaching a graduate level potential field course this semester at UH. My students and I are developing some open educational resources for this course. It is sort of like a textbook but not quite. It is more like commentary of the lectures I give in class. Here is the link to the resource https://uhlibraries.pressbooks.pub/geophysicspotentialfield/. We do use some materials from geosci.xyz.
It is far from being considered as good. There is a lot more to do. Specifically, many contents need to be further expanded. Many new contents need to be added. Most importantly, we need to develop a lot of interactive tools so that students can play to develop a better understanding of potential field data (theory, processing and interpretation techniques/methods). One good starting point is to convert the Fortran in Appendix B in Blakely’s book to a set of interactive tools.
I hope more people from SimPEG community and grav/mag community can join in this effort.