They have a list of requirements on the about page that basically boils down to "any open source software that you authored which has a research application". There's more detail about the requirements in the reviewer guidelines, which mostly have to do with the development best practices: documentation, test suite, contributor-friendliness, etc. And they also give Fidgit as an example paper on the about page.

For your particular examples, I would say the rat hippocampus simulation almost certainly fits their guidelines, and the Django packages probably don't, unless they're doing some sort of scientific computation or data visualization.