Great source of peer-reviewed textbooks. Tend to lean more toward the sciences.
Usually have additional resources such as ppt slide shows and tests to go along with textbook.
Many are adapted and available in Canvas Commons
Founded in 2002 by Nobel Laureate Carl Wieman, the PhET Interactive Simulations project at the University of Colorado Boulder creates free interactive math and science simulations. PhET sims are based on extensive education research and engage students through an intuitive, game-like environment where students learn through exploration and discovery.