Q:

Granular document management and creation tool

I'm looking for a document or content management tool - I'm not quite sure of the generic name for the tool I'm looking for**. 
Our use case is creating collection of documents each of which offer different view of a product catalogue - each with similar contents but aimed at different audiences.
A sightly simplified description of our requirements are; We'd like to be able to maintain a public and internal edition of the document.  The internal edition would be more detailed than the public edition. The main part of the document will be approximately 20 chapters. One chapter per product. Each chapter will have a common set of paragraph headings. The public edition should be automatically created by a set of rules which select a subset of the paragraph headings from the master document. We expect to create many iterations of the master document so the process of deriving the public edition must be easily and quickly repeatable.
In reality we may need more than just two different editions of the document. But the same workflow should be repeated - all editions other than the master can be automatically derived from the master copy. Only the rule set would change between editions.
Some additional preferences:

Ideally the rules for defining the public edition should be easy to manage, though a small amount of scripting is acceptable.
Cloud based would be ideal but not essential. We are mostly windows based if locally installed software is required. 
We are a charity so free or not too expensive.

Many thanks.
** If I google "document management" most tools are about either scanning or managing and indexing large numbers of whole files. If I google "content management" most tools are website frameworks. I'm not sure of the right search phrase to get the kind of sub-document granular control I'm looking for.

A:

The standard: DITA
DITA is a standard for generating several documents from a single source.
For instance, a company that makes kettles might have:

A general presentation of the company
A warning about the risks of kettles
A description of SuperKettle
A description of the features specific to the Deluxe version of SuperKettle
A description of MiniKettle
A catalog of all kettles

All of these parts are DITA fragments.
To generate the SuperKettle Deluxe manual, you would use a DITA tool that takes all of the relevant parts and combines them into a single document.
An implementation of the standard: DITA Open Toolkit
DITA Open Toolkit is an open source implementation of the DITA toolchain.
It is written in Java and runs on Windows/Mac/Linux.
User guide: http://www.dita-ot.org/2.1/user-guide/transforming-dita-content.html
The parts themselves must be written in Docbook or in the DITA-specified XML, at your choice. Both formats have some WYSIWYG editors available.

