World-famous Harvard University currently offers 42 of its classes for free online. Many of these classes on edX, like Introduction to Computer Science, are self-guided and ready to start anytime you’re are. Others, like AnatomyX, run on a fixed schedule. Some even offer college credit through the Harvard Extension School for a fee; otherwise, completion earns you a nifty free ‘Honor Code’ certificate. You can browse Harvard’s online course listing at edx.org/school/harvardx.