Browser as a rich client platform

Browser as a rich client platform

In Java there is a notion of "rich client platform" - it's a framework for
building desktop applications, provides common features like help browser,
window layout management, etc. Prominent frameworks are Eclipse and
Netbeans.
Now I am curious if something like that can be done on top of web browser?
I heard about XULRunner, Chrome extensions, NPAPI and such but hesitant to
dive further (my current idea is to fork Chromium).
Basically, is there a way from a (serverless) browser application:
Work with filesystem (Open/Save/open OS file browser)
Start OS processes (e.g. some utilities) and parse their output.
Access dynamic libraries.
Alter browser UI (e.g. remove home/address bar, redo menus)
Package as something easily deployed throw the app stores.
Can this be done without forking the browser? What should I read about?
Updated Requirements: Essentially I am looking for "PhoneGap for PCs" -
but I really like how I could reuse Chromium UI (tabs, preferences, etc)
if I forked it. I'm prototyping on Mac, will setup a Linux build. I am not
interested in Windows at this point...