djangotoolbox | Django tools for building nonrel backends

The -m option to python allows you to (try to) run a module/package. From the docs:

-m

Search sys.path for the named module and execute its contents as the __main__ module.

Since the argument is a module name, you must not give a file extension (.py). The module name should be a valid absolute Python module name, but the implementation may not always enforce this (e.g. it may allow you to use a name that includes a hyphen).

Package names (including namespace packages) are also permitted. When a package name is supplied instead of a normal module, the interpreter will execute .__main__ as the main module. This behaviour is deliberately similar to the handling of directories and zipfiles that are passed to the interpreter as the script argument.

So, the thing following -m needs to support being run by defining a __main__, which is why python -m pymongo then states "No module named pymongo.__main__".

For the case of Django, or specifically, django-nonrel: It looks like django-nonrel hasn't been updated in years, and the most recent branch looks like a fork of Django 1.7. Django proper added django.__main__ in 1.9, so that's why the docs you're reading are misleading you. You might be able to use the Django 1.7 tutorial, but a NoSQL database might heavily affect the models and queries, so using the tutorial provided by the nonrel project (if it does) would be preferred.