I've read about Flask blueprints, but that didn't seem to have the same angle... seemed to be more shippable libraries rather than a module of an application.
[1] Not python modules. I say module in the abstraction sense.
For eg, you can create a blueprint comments, define url rules('/', '/new', ':id/edit'...), add authentication to before handler(check before create, delete, edit), and then mount it on the main application.
app.register_blueprint(comments, url_prefix='/comments')
You can have blueprints which are self contained modules(comments), blueprints which just add jinja extensions, blueprints which bring in static assets etc etc. What does Django apps do which blueprints don't?