Online course providers like edX and coursera offer free courses, but you can only take/enroll the courses at specific times of the year (not any time). Why is that? If you just want to learn something (not for a degree in accredited institutions), it would be much easier if you could do it online anytime.
Actually for both of them some courses are fully autonomous "anytime" courses, while others are restricted to being offered at particular times. So far as I can tell, the time-restricted courses derive two benefits from being time-restricted:
- It creates a "cohort" of students learning similar things and doing similar assignments at the same time, who can then help one another in the associated forums.
- Resources needed to support the course (e.g., TA monitoring, course material updates) can track the progress of the students through the course, increasing the return on resources and minimizing disruption to students.
You kind find two type of courses.
Self-paced: When you select this type of courses you can enroll and take these courses any time of the year.
But the live courses will enable you to enroll only twice or thrice a year. This is because this type of courses will be conducted for large amount of students at the same time. That's known as MOOC-Massive open online course.