PhET provides free interactive simulations for physics, chemistry, biology and mathematics that visualize scientific concepts.
Open Textbook Library is a repository of freely available textbooks across multiple disciplines that can be downloaded and adapted.
Scholarpedia is a peer-reviewed online encyclopedia with physics articles and academic references.
A collection of informal explanations and demonstrations of classical physics phenomena and electrical engineering.
Online physics and chemistry instruction with interactive tools for students.
Michael Nielsen's personal notes and essays on quantum computing, quantum mechanics, and physics.
Freely available introductory and advanced physics textbooks covering mechanics, waves, electromagnetism, and modern physics.
Collaborative wiki covering mathematics and physics topics with formal definitions and relationships.
Site explaining vector calculus and mathematical concepts with visual intuition.
Physics Hypertextbook; online reference covering classical mechanics, electricity, optics and modern physics.
OpenStax CNX hosts peer-reviewed open textbooks in physics, mathematics, and other sciences that can be read and adapted freely.
Interactive visual explanations of physics concepts through play-based learning.
Personal website by physicist John Walker with educational essays, calculators, and explorations of physics phenomena.
Online reference covering numerical methods, special functions, and mathematical physics.
Personal interactive visualizations and explainers for physics and mathematics concepts.
Hypertextbook covering mechanics, waves, optics, electricity, and modern physics with problems.
Wolfram's NKS explores cellular automata, complexity, and computational processes in physical systems.
Introductory college physics text and problems.
Fizalis is a Russian physics education website offering theory, worked examples, and problems across classical and modern physics.
Russian physics encyclopedia providing definitions, formulas, and reference material.
Collection of interactive visual demonstrations and problems in mathematics and mathematical physics.
Russian educational encyclopedia covering many subjects including physics.
Host of searchable physics textbook PDFs for secondary and first-year study.
These are filed under other headings but serve this one too.