Open2study

Open2study provides free short courses, entirely through online mode, across the world, in a range of subject areas such as Physics, Chemistry, Biology ..etc. You can register free of cost and can choose any of the course, after completion of a course you will get an achievement certificate, but, you can not use that certificate for any further enrolment.

You get a note on the certificate that state "Open2Study subjects are not equivalent to accredited tertiary or higher education subjects.Completion of the subject does not confer credit or advanced standing towards any subject, course or qualification.This certificate cannot be used to affirm that the student was enrolled or studying directly with any educational institution delivering a subject through open2study "

However, this is a very good website to learn about a variety of subjects.