Edx.org is an initiative by a group of universities where they offer free online courses to anyone in the world, regardless of age or their field of expertise.
As said, the courses provided are free of cost while you have to pay a small amount of sum if you wish to procure a certificate for your newly learned skill. This certificate is not necessary and would not affect your course and your marks in it.
The courses varies from computers to arts and ever philosophy. So content should not be a problem.
I use it for building my computing expertise by learning new languages and coding, which I find interesting and enjoyable.
Courses consist of video tutorials followed by quiz and questions, which is quite interactive.
I would like to summarize, if you want to learn something new, which intrigues you then I would definitely recommend edx.