MOOC stands for Massive Open Online Courses.  Online environment is changing continuously and it represents a great opportunity for learning. Access to free courses has allowed students to obtain a level of education that many only could dream of in the past.  This has changed the face of education. 

Advantages:

- you can chose any place and time to study

- almost unlimited number of topics to study

- possibility to combine job and study

- you can get cources from the best masters for free

Disadvantages:

- need high level of motivation and discipline

- luck of social comtext

- learning from a computer screen

As for me the best platforms for online learning are:

Harvard Extension School

Personaly I like the idea that I can take any course of the best professors in the world for free. They are really very interesting. Moreover it's a great opportunity to listen to wonderful British English. There are more than 900 free-courses about almost everything. There are various course formats so everyone can chose one that will work best with his or her schedule.

Open Yale courses 

I found of it because all lectures were recorded in the Yale College classroom and are available in video, audio, and text transcript formats. So you can feel as you are at a lecture at one of the best universities in the world.  And registration is not required. You don't need spent time to register. Open Yale Courses provides free and open access to a selection of introductory courses taught by distinguished teachers and scholars at Yale University. The aim of the project is to expand access to educational materials for all who wish to learn.