This question is inspired by the popular "Best Sets of Lecture Notes and Articles".
Indeed, I would like to collect a "big-list" of open source (that is, with $\LaTeX$ code available) high-quality (according to strictly mathematical and pedagogical standard) lecture notes or textbooks on as many mathematical topics as possible.
Note that here the focus is only on open source lecture notes or books (which could help students to create their own notes for self-study more easily by modifying existing works).
Among the many other topics that I would like the material to cover, in particular I am currently interested in:
- real analysis;
- complex and functional analysis;
- abstract algebra;
- linear algebra;
- number theory;
- general physics;
- mathematical physics (mainly classical mechanics);
Update: I am thankful for the answers provided so far, and I encourage to share here more examples of good opensource material in the areas which have not been covered.