Qt Assistant
From qtnode
Introduction
Qt Assistant is a tool for presenting online documentation. It is mostly used to show the Qt Reference Documentation, but can actually be used to show other documentation as well.
Qt Assistant Tips and Tricks
A collection of Qt Assistant tips and tricks that may be of some use: Qt Assistant Tricks
How to use Qt Assistant as an application's help tool
There is a good documentation on how to use QAssistantClient at: http://doc.trolltech.com/latest/qassistantclient
A simple and straightforward example is shipped with Qt: http://doc.trolltech.com/latest/assistant-simpletextviewer.html