A tool for converting graphie JS code to a png image, available at http://graphie-to-png.khanacademy.org/.
Khan Exercises is very out of date. This is because graphie-to-png will not work after some changes made in January, 2015. See this support ticket for more information.
Upgrading Khan Exercises would be a fairly large task, so you may want to consider other alternatives instead (like cherry picking into the graphie-to-png branch of Khan Exercises).
To run this locally, fill in secrets.py using the template at secrets.py.example then run python app.py.
Fill in secrets.py once again then run ./server.sh in a screen or something along those lines. (TODO(alpert): Create a launchd config or something.)