Django: Put a Form into a Form (recursive ...)
In first glance, your idea seems to be complex. And the immediate question is - "Why do need such feature?". 99% - of tasks can be solved with built-in Django "bricks", another 1% - "Please hardcode". Also I may assume that the problem behind such an idea is complex too, and will be hard understandable by end user.
I like Django forms library, but it would be even better if a form could contain forms.
My dream looks like this: 

I have a form which behaves like normal form: for example a class called SuperForm
SuperForm can contain several normal forms, or even (recursive) SuperForms
You can bind it to data (to make it bound), call is_valid() ...

Is this possible with django or an external app?
Update
I see many people did not understand what I want. My fault, I did not give a use case.
Use case: A page should allow the user to update his email and his telephone number. The email is from django.contrib.auth and the phone number is from our custom model.
Both inputs should be in a single <form> tag. Since ModelForm is easy to use, I don't want to create a form myself by hand.
I want a container which contains the ModelForm of django.contrib.auth.models.User and the ModelForm of our custom model.
I don't want to loop over both forms (in other use cases there could be much more forms) myself, and check whether they are valid or not.
If I call is_valid() or save() on the container the matching method of the forms gets called.