The Open edX Platform is made up of multiple web services that work together to provide all the tools you might need to build and run courses online.
While there are a few exceptions, for the most part the technology stack for the Open edX Platform uses Django for backend services and React for the frontend. The frontend consists of multiple frontend apps which are usually referred to as MFEs (Micro-FrontEnds) within the ecosystem and community.
The core code base lives on GitHub in the openedx organization.
While the platform contains many services such as MFEs and libraries, the core of the platform lives in the edx-platform and frontend-platform repositories.
edx-platform - This was the first service created in the Open edX ecosystem and contains the legacy monolith application. That application currently can run in two modes: LMS and Studio.
As the LMS (Learning Management System), it acts as the backend for learners’ data as they go through courses and programs, and it serves some legacy UI elements.
As Studio, it is the CMS(Content Management System) where instructors and course authors can build the course content that learners will consume.
frontend-platform - This is a newer core system meant to ease the creation of multiple MFEs by bundling together many common utilities that all frontends need. This includes things like authentication workflows, logging, monitoring and translations related tooling.
In addition to the backends and frontends mentioned above, the platform is made of numerous libraries that live in the openedx organization. These libraries accomplish a variety of different tasks. More details about what they do can be found in their READMEs.
While the above summary covers most of the system, there are a few exceptions.
The cs_comments_service which provides discussion forum capability within the platform is a legacy application that is written in Ruby, using the Sinatra framework.
The Open edX Platform is currently still in the process of moving to React based MFEs. Previously frontend content used to be served by the Django services. This means that there are still many parts of the system that use Django Template based rendering pipelines to serve frontend content to users.
An exception to the expception. In edx-platform rather than using the default Django templates, django is setup to use Mako based templates.