Publicly available lecture notes from universities mathematics classes

https://www.reddit.com/r/math/comments/9s5548/what_are_your_favorite_publicly_available_notes/

http://math.stanford.edu/~vakil/216blog/   

https://www.reddit.com/r/math/comments/4nbqag/lets_make_a_collection_of_lecture_notes/

https://dec41.user.srcf.net/notes/

https://www.reddit.com/r/learnmath/comments/98wwfv/undergraduate_lecture_notes_university_of/

https://www.reddit.com/r/math/comments/csgigv/collection_of_lecture_notes_on_mathematics_and/

https://www.maths.cam.ac.uk/undergrad/studentreps/tripos-specific-resources 

https://www.maths.cam.ac.uk/notes-web