Open edX uses both the AGPL and the Apache license. The code in Open edX is spread across a number of repositories on GitHub, and each is licensed under either the AGPL or the Apache license.
The AGPL (GNU Affero General Public License) is maintained by the Free Software Foundation. It allows for use and sharing of unmodified code, modifying code, and the use and sharing of modified code.
Under the AGPL, when you modify the Open edX platform, you must share those modifications.
The Apache License is maintained by the Apache Foundation. It allows for the same use, sharing, and modification as the AGPL, but modifications can be shared under a license other than the AGPL.
The Open edX code falls into three main categories: core components of the Open edX platform, libraries used by others to access the platform through our APIs, and tools that are not particular to the Open edX platform. Each of these categories has its own licensing considerations.
Code that is essential to the Open edX platform is AGPL. This license ensures that all changes to the platform are shared, guaranteeing that the platform is truly an open resource and that everyone will benefit from the improvements. This includes, but is not limited to:
Code that is used by others to access edX APIs is Apache. The propagating nature of the AGPL makes it difficult for some people to adopt. For repositories where broad use is more important than shared improvements, edX uses the Apache license. This includes API libraries such as XBlock.
Broad-interest, or developer, tools are also Apache. These are tools that have nothing in particular to do with Open edX, and do not run as part of the platform. They could be of interest to any Python developer, for example. Tools like this will be Apache-licensed to enable their broader use and adoption. This includes tools such as bok choy.
To figure out which license a given repository uses, read the licensing file contained in the GitHub repository.
If you have any questions about edX's licensing strategy, feel free to ask on the edx-code mailing list.