This page demonstrates a generic Numbas runtime which can load any .exam file.
There's a static copy of all the runtime code and the default theme's templates.
Extensions and custom part types work, but I need to think about how question resources should work. It might need some URL-rewriting trickery.
Try it on an exam file
Some I prepared earlier...
After the page loads, the list below will be filled with published exams from numbas.mathcentre.ac.uk.