This incredibly comprehensive site offers 24 free online modules that explain a wide variety of concepts within electrical engineering. Each module is presented in a style similar to that of a textbook, with detailed explanations of concepts, discussions of underlying theory, and practice problems with solutions. Topics include electromagnetics, digital computers and logic, fiber optics, and many more. Despite the depth of this site, there are some minor downsides that should be noted. First, printable versions of the modules can only be downloaded after paying a fee. The only other issue is a floating advertisement that, while tucked away in the bottom corner of the page, can be somewhat distracting.