Udacity was founded by two professors at Stanford University (Prof. Thrun ve Prof. Norvig). They started Udacity in August 2011 just after they reached the number of 160,000 people when they offered their Artificial Intellegence class online. Udacity devoted themselves more to Computer Science classes. Most of their online students are people who work in IT departments.
They have Computer Science courses at every level, though some courses are not free, please pay attention when choosing your courses.
Pictures from campus of Princeton University