Poco is a C++ framework suited to network server and web application development. It has fairly good documentation but it's presented as old-style HTML frames, so it's missing a lot of features I like with Qt.
So I converted the Poco docs into a Qt Assistant format help file, with index, table of contents, full text search, tabbed browsing and working history.
To use it, download pocoqthelp.zip, and unzip it to give poco.qhc and poco.qch.
If you don't have Qt Assistant installed already, install it from qt-project.org or (on Linux) as a standard system package.
Then launch Qt Assistant as "assistant -collectionFile poco.qhc". On OS X you'll need to run "/path/to/Assistant.app/Contents/MacOS/Assistant -collectionFile poco.qhc".
The zip file also includes makeqthelp.pl and poco.qhcp, which can be used to rebuild the Assistant help files from the Poco HTML documentation.