Ignoring the currently trendy InterCap names, here you get MIT- (and other university)-level courses. OpenCourseWare came first, years ago, as a free repository of curricular materials from actual MIT courses. Originally, the material found on OCW was spotty, sometimes only a few syllabuses posted, or perhaps the final exam. Part of the concept was to provide material for other teachers around the world, more than for other learners.
But as time went on, OCW added video and audio of some of the courses, such the very popular Classical Mechanics course. Some classes have entire, free textbooks posted. I have used the OCW site for years for reference material for myself, as well as to help me teach some other concepts.
But there were things missing from this experience compared to regular college courses. Sure, you could download assignments or tests, but it's not like anybody would grade them.
Enter edX, which provides online courses, with assignments, labs, and exams -- the whole schmeer. This is serious stuff, though, with real timetables and deadlines, unlike with Udacity. And the timetables seem to line up with regular college semesters, which is a weakness to a certain extent.
The courses are free, and like with Udacity, there is talk of getting certification for a nominal fee in the future, which is not yet implemented.
I tried out 6.002x when it was first launched as MITx, but only got a few weeks in. It was just a large time commitment, having to go by this schedule... and it really wasn't fun to me. But if you want serious college courses from top notch universities, this is a great way to try them out for free.