WinHelp

AuthorIT
Tour of main features, free trial version of this tool. Also detailed product information, examples, support pages, user forum.
http://www.authorit.com/

EasyHelp
A development tool that creates help files from Microsoft Word documents. FAQ, mailing list, free trial download.
http://www.easyhelp.com/

ForeHelp
Supports various formats. Customer testimonials, monthly newsletter, screenshots, FAQs, free trial downloads.
http://www.sinterphase.com/fhintro.htm

Help to RTF
Help to RTF's converts Windows helpfiles into RTF-formatted document files compatible with Word. The converted RTF documents include the associated BMP, WMF, SHG and HPJ files.
http://www.herdsoft.com/catalog/ehlp2rtf.html

HelpBreeze
A WinHelp, HTMLHelp and HTML help authoring program.
http://www.solutionsoft.com/hlpbrz.htm

HelpHikes Pro
Create detailed, non-trivial help files for Windows. Drag and drop links between your topics and test them at design time. Manage big help projects easily with the unique hypertext folder-based approach.
http://kanadepro.com/helphikes/

Helpmatic Pro
WinHelp and HTML help authoring tool for creating professional help files quickly. FAQs, reviews, download trial, ordering information, and upgrades.
http://www.helpmatic.net/

HyperText Studio
A visual HyperText authoring package which makes it easy to create and manage Windows Help files, Web sites and HTML Help files.
http://www.olsonsoft.com/

Instant Help Pro
A generator and editor for WinHelp and HTML Help. It automatically creates the help system and updates the source files and project files of a Visual C++ Project.
http://www.georgscheidel.de/html/inshelp1.htm

Sevensteps
Development tool delivers plain HTML and WinHelp from one XML source. Free trial version available.
http://www.sevensteps.com/

Software Interphase
Authoring system including ForeHelp, Help Magician Pro, and WinHelp Sorcerer.
http://www.sinterphase.com/