Extending edX Platform

This table summarizes the types of extensions that are currently supported by the edX Platform:

Extension Type	Description	Current Support
Courseware component types	Use XBlocks to create new types of components that can be included in a course.	XBlocks documentation
External graders	Host an external grader separately from the edX platform.	External Graders
LTI applications	Add external learning applications or digital textbooks.	Open edX LTI documentation
Custom problem types	Add a new type of problem by including custom JavaScript.	Custom JavaScript Applications
LMS course tabs	Shows a new tab to the user when they are viewing a course.	Adding a new course tab
Studio/LMS page	Add a new page to Studio or the LMS. Note that this currently requires making changes directly into the edX platform.	How to add a new page to LMS or Studio
User partition schemes	Add a new scheme that will partition users into one of a set of groups.	/wiki/spaces/PT/pages/11927648

Useful links

There is more detail in the edX Developer's Guide: Options for Extending the edX Platform.
Web Fragments describes how to build pluggable user interfaces.
Feature Plugins for edX Platform describes how the platform could be extended to support feature plugins.
How to add a new feature to LMS or Studio describes the steps necessary to implement a new feature as a separate Django app.
How to add a new plugin entry point to edX platform describes how to go about providing a new type of plugin.