Open edX was written by the edX nonprofit organization created by MIT and Harvard. edX.org is the largest instance of open edx. Open edX is the open source platform that powers edX courses.  On June 1, 2013, edX open sourced its entire platform.
The platform is written in Python and uses other free and open source platforms like Django, MySQL, jQuery, Mako etc.
Open edX consists of two primary pieces of functionality:
LMS - Learning Management System
The LMS is the component that students use to participate in the course. The LMS consists of videos, notes, lectures, discussion forums, assignments and quizzes.
Studio is the Open edX sophisticated online course creation and publication tool. It allows instructors to create custom online courses, control publication and access as well as provide insights into how the learners are fairing in the course.
Open edX Stats as of June 2018
1500+ sites using Open edX
18,000 + courses
18,000,000 Open edX learners https://youtu.be/ZvJpdRWLA_w?t=64