edX courses tend to be slightly more academic and challenging than those of its most obvious competitor, Coursera. All courses still have the option of free certificates although verified certificates are now also offered.
It is obvious that the platform designers put considerable thought into the course presentation, unfortunately, it sometimes seems that they tried too hard. For all the neat user interface bells and whistles, Coursera's 'plain and simple' menu navigation system still ends up being easier and more intuitive.
A good example of this is the contrast between the forums on the two platforms. Coursera's forums seem to foster a much more active learning community with thriving discussions while edX tends to generate highly repetitive one or two post threads to which the software almost actively discourages the student from returning.
edX's 'Courseware' strip-based navigation seems rather awkward at first but is stronger than Coursera in allowing the integration of mixed media (eg readings, discussions and practical activities alongside video lectures). One adverse side effect of the navigation system is the increased complication for those who want to download the lectures. The user must scroll through each part to find and download the videos (where available--not all offer downloads) rather than the single 'Video Lectures' page normally seen on Coursera, for example.
edX also offer multi-course sequences (XSeries) which combine a number of courses, usually from a single provider, and issue an overall certificate. Unlike the Coursera Specializations, there are no capstone projects or additional assessment beyond that included in the individual courses. All courses must be taken on a Verified basis and there is an additional fee for the issuing of the series certificate.