WebHelp
WebHelp has similar functionality to Microsoft CHM help. There is the familiar tri-pane navigation (which can also include, for example, a Glossary tab).
WebHelp is cross-platform help that runs on Windows, UNIX, Mac OS, and other operating systems. Basically, it is HTML with JavaScript. The user needs only a web browser to view the help.
To create WebHelp, a technical writer uses the RoboHTML (or the RoboHelp) software from Adobe (www.adobe.com). Visually, WebHelp is attractive. From a technical perspective, a serious flaw is that the help files contain code that does not conform to the W3C specifications.
See also 
Comparison of online help formats
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