Cross-platform end-user-help authoring tools

What are some good authoring tools for creating cross-platform help files for end-users? (Our application is using the Qt framework, if that makes any difference.)

Note: I'm not interested in internal API documentation--we're using doxygen for that.

Ideally, a solution would:

• Allow us to manage all help content (text, table of contents, images, etc.) in a single location.
• Output to native help formats. (CHM for Windows--or at least something we could feed directly into the HTML Help API; not sure what other platforms' "standard" help formats are.)
• Decent WYSIWYG support: handle common text entry, images, cross-references, etc. easily, but we can edit the HTML when we need to.
• Text-based file-format for help project (XML, etc.) so that it can be versioned in Subversion.
• Any hooks that help keep it in synch with the actual code base would be great. (Perhaps somehow a help topic is associated with a code file, and can check Subversion to see if any changes have been made and flag a topic as "possibly out of date" ... am I dreaming?)
• Help content can be localized.
• Not opposed to commercial product, but a free option would be nice.

I'll go ahead and make this a wiki and start with a few examples. Vote 'em up or down if you have experience with them, and leave some comments. Add additional tools as well.

I just discovered Sphinx; I think I'm in love.

• Better than WYSIWYG over HTML: reStructuredText
• Outputs to QtHelp (among other things), so will be easily to distribute (and integrate) in our application.
• Not sure about localization yet, but we'll cross that bridge when we need to.
• Was easy to set up and "just works"; looks professional.