edX is a non-profit, massive open online course (MOOC) provider. The majority of edX courses are entirely free to access and most also offer an optional verified certificate track for a fee that varies per course. Courses may consist of video and text content, discussion forums, and a number of problem and assessment types.
A range of free, open, online courses from leading UK Universities.
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.