Development specialized on the free software project Open edX, used by many universities and companies to run online courses. See edx.org, stanford.edu or fun-mooc.fr for examples of Open edX instances.
It's a large Python/Django codebase, with good code standards and architecture (a lot of the edX engineers come from MIT). You would work on different clients contracts using the platform. The clients list/references include Harvard, edX themselves, the French government, and various universities & companies currently running their own instances, or looking to create one. Tasks are varied, from developing developing core platform features, custom exercises and tools for specific courses (XBlocks), customizing and deploying instances, working on both client/server sides, etc.
Most of your work is published as free software (Open edX is released under the AGPL license, which requires clients to release modifications under the same license), and you would also contribute to the free software project, pushing some of your developments upstream through pull requests, contributing features, documentation or help on mailing-lists.
Optional requirements (you would be able to pick it up on the job if you don't master this yet):