Free Books on Physics

Online course on topology in condensed matter

Feynman lectures

Electrodynamics by Phil Nelson (excellent!)

Understanding the Properties of Matter by Michael de Podesta

Entropy by John Baez

Group Theory in Physics: An Introduction with Mathematica by Balasubramanian Ananthanarayan, Souradeep Das, Amitabha Lahiri, Suhas Sheikh, Sarthak Talukdar

Lecture notes on Statistical Physics by Lydéric Bocquet

Lecture notes on Soft Matter and Interfaces by Lydéric Bocquet