* Registering models with the admin
* Registering models with databrowse
* Registering template tags
* Registering custom management commands

It's also present in popular party apps:

* django-tagging and django-mptt both register models (though both
feel like they should really be some kind of mixin)

We'll also need it in the near future for a couple of in-development
features:

* Registering custom panels with the Django debugging toolbar
* Registering new benchmarks with the metronome profiling tool
* Registering get_connection overrides in the above multi-db proposal

Finally, we've been needing to solve it for projects at work: we have
a CMS that exposes a concept of "custom rows" which can be provided by
applications and dropped in to various places around the site. Guess
what: the rows need to be registered!

There MUST be a good way of doing this. zope.interface? setuptools
entry points? We really, really need to solve this for Django. If we
had a single, supported and documented way of registering things it
would open up a huge amount of potential for plugin-style extension
points and give us a proper solution to a problem we are solving in a
bunch of different ways at the moment.

Any ideas?