Mutli-User & Multi-Subject Drupal

I have been trying to see if a module exists already or not for this purpose. More or less, I want to create an internal intranet site for my company. The issue, is that I want separate sections for each department. In essence, one core front-page for company wide announcements and navigation. And then on top of that have these sections for each department.

Those sections obviously would be viewed by everyone, however only edited by those who SHOULD edit for a given department/section. I also want each department to have the ability to do their own pages, stories, blogs etc. In essence it would be like mini websites for each departments where they can post stories on a "front page" of their section, and also add their static pages for other content as well.

From what I have seen of Drupal so far, you can have multiple users on one site, but in essence the overall "topic" of the site is the same. Stories only can be posted to the front page, and being able to setup URL structure seems almost insane.

Regarding URL structure.

In essence I have http://example.com

example.com has the "main" stories page for the company, and then some relevant data and a menu that lists each department.

Then I can do something like http://example.com/departments/depA, http://example.com/departments/depB, etc, etc

But also be able to do http://example.com/departments/depA/about, http://example.com/departments/depA/contact, http://example.com/departments/depA/blog, etc, etc....

Is there an easy way to establish this, or am I somewhat up the proverbial creek?