Alexandre Stefanov long maintained a list of online math texts and other materials at Geocities, but it appears that his original web site is no longer available. Because these resources may be of interest to our readers, we present here a modified version of Stefanov's list as of November 18, 2009. We welcome corrections or suggested additions to this list.

See also Math on the Web, compiled by the American Mathematical Society, for more online math resources.

Dynamics

• Mechanism of the Heavens (1831), by Mary Somerville. This second edition was prepared by Russell McNeil
• Dynamics in One Complex Variable: Introductory Lectures, John Milnor
• Geometrical theory of dynamical systems, by Nils Berglund
• Introduction to Statics and Dynamics, by Andy Ruina and Rudra Pratap

Entropy

• Entropy on the World Wide Web, has links to expository articles, journals, software, and conferences pertaining to entropy.
• Entropy of Compact Group Automorphisms, by Thomas Ward
• Valuations and Hyperbolicity in Dynamics, by Thomas Ward
• Effective Hamiltonians and averaging for Hamiltonian dynamics, by Lawrence Craig Evans
• Entropy and partial differential equations, by Lawrence Craig Evans
• CLASSICAL AND QUANTUM CHAOS, by Predrag Cvitanovic
• Dynamical systems, by Shlomo Sternberg

Quantum Mechanics

• Mathematical Methods in Quantum Mechanics, by Gerald Teschl
• Quantum Mechanics, by Klaus Schulten
• Foundations of Quantum Mechanics & Quantum Information, by M. B. Plenio
• Quantum Geometry and more, by Micho Durdevich
• Quantum Probability Theory, by Miklos Redei, Stephen J. Summers

Quantum Field Theory

• Comprehensive textbook on quantum (and classical) field theory, by Warren Siegel
• Quantum Field Theory, by Ben Simons
• Mathematical ideas and notions of quantum field theory, by Pavel Etingof
• Introduction to Algebraic and Constructive Quantum Field Theory, by John C. Baez, Irving E. Segal and Zhengfang Zhou (scanned pdf. extermely big 200 megabytes)
• Lecture Notes from the Quantum Field Theory program at IAS, 1996-1997
• Graduate textbooks: Field Theory, Relativity, Superspace, Strings, by Warren Siegel
• Introduction to String Theory, by Igor V. Dolgachev
• What is String Theory, by Joseph Polchinski
• Operator Algebras and Quantum Statistical Mechanics, Volumes I & II, by Ola Bratteli
• D-Brane Primer, by Clifford V. Johnson
• Introduction to Superstring Theory, by Elias Kiritsis
• Algebraic Quantum Field Theory, by Hans Halvorson and Michael Mueger

Condensed Matter

• Worked examples in the Geometry of Crystals, by HKDH Bhadeshia
• Concepts of Theoretical Solid State Physics, by Alexander Altland
• Many-Body Physics, by Piers Coleman
• Theory of Superconductivity, by Helmut Eschrig
• High-Temperature Superconductivity, by Peter Hirschfeld
• Solid State Physics, Notes, Problem Sets, & Tests by Peter Hirschfeld
• Complex Surfaces in Materials Science, with few books
• Photonic Crystals: Molding the Flow of Light, by John D. Joannopoulos, Steven G. Johnson, Joshua N. Winn, and Robert D. Meade

Special and General Relativity

• General Relativity, Nonlinear PDEs, etc., Sergiu Klainerman
• Special Relativity and Geometry, by C. E. Harle, R. Bianconi
• Lecture Notes on General Relativity, by Sean M. Carroll
• General Relativity and Quantum Cosmology, by Sean M. Carroll
• Public lectures by Stephen Hawking

Physics

• Essential Physics 1, by Frank Firk
• Introduction to Groups, Invariants & Particles, by Frank W. K. Firk
• Classical Electrodynamics, by Bo Thidé
• Classical electrodynamics and theory of relativity, by Ruslan Sharipov
• Electromagnetic Theory and Computation: A Topological Approach, by Paul W. Gross and P. Robert Kotiuga
• MOTION MOUNTAIN TEXTBOOK Hiking beyond space and time along the concepts of modern physics, by Christoph Schiller
• Fundamentals of Thermodynamics, by J. Karl Johnson
• Non-Equilibrium Statistical Mechanics, by Klaus Schulten
• Course in Electrodynamics, by Franz Wegner
• Light and Matter, by Ben Crowell
• Order-of-magnitude-physics, a book by Sanjoy Mahajan
• A Brief Introduction to Physics for Mathematicians, Igor V. Dolgachev
• Physical Applications of Geometric Algebra, by Anthony Lasenby and Chris Doran
• Group Theory for Physicists, by Predrag Cvitanovic
• An Elementary Introduction to Groups and Representations, by Brian C. Hall
• Geometric Models for Noncommutative Algebras, by A. Cannas da Silva and A. Weinstein
• Differential Forms in Electromagnetic Theory, by K. Warnick, R. Selfridge and D. Arnold
• Lectures on integration of several variables, by Michael Adler
• Concepts in Theoretical Physics, by Ben Simons
• Further Mathematical Methods, by Niels Walet
• Computational Physics, by Angus MacKinnon
• Zeno meets modern science, by Zurab K. Silagadze
• Feynman's derivation of Maxwell equations and extra dimensions, by Zurab K. Silagadze
• TeV scale gravity, mirror universe, and ... dinosaurs, by Zurab K. Silagadze
• Quick introduction to tensor analysis, by Ruslan Sharipov