Self-learning online has become very popular and there are several sites offering courses to learn a wide range of topics. For a project I needed to get an overview of some of the most popular sites and created the below matrix. Here it is for all of you to read, please let me know if you find something incorrect. Of course this is not a complete listing of all such sites, Futurelearn and iversity among others were left out, but the table still contains the biggest ones.

 CourseraedX Khan
LyndaSkillshare treehouse Udemy
CostFreeFreeFree$20-$35 per monthFree to $10 per month$25-$49 per monthFree to $300 per course
Course completion certificatePaidPaidNoYesNoNoYes
Type (mooc, etc.)MOOCMOOCVideo libraryVideo libraryVideo libraryVideo libraryVideo library
Users10 million4 million10 million4 million0.9 million0.1 million8 million
Mobile appsAndroid and iOSAndroid and iOSAndroid and iOSAndroid, iOS and WindowsAndroid and iOSAndroid and iOSAndroid and iOS