Coursera is maybe not a great example - they don't even vet their courses before starting to sell them, and they won't necessarily offer refunds if you want to drop a disappointing course partway through. It's full of courses with two weeks of 'intro' material which references the exciting things which will (not) be taught in future weeks, and it seems more like a diploma mill or collection of half-baked blog posts than any sort of real education. I've had overwhelmingly negative experiences with them.

EdX is a quality platform, though, and MOOCs in general could fill that role.