The way Numbas tests are displayed is separated from the underlying control code, so you can completely change the way a Numbas test looks.
You can make changes ranging from small details like the logo and colour scheme, to completely overhauling the rendering of the test. For example, the “printable worksheet” theme generates any number of randomised exams ready to be printed out, with accompanying answer sheets.
More advanced users can write extensions to add new functionality to Numbas tests.
For example, some of the extensions developed at Newcastle University add support for statistical distributions and tests; add new data types representing elements of permuation groups; and allow the integration of interactive graphics using the open-source library JSXGraph.