Alternative to helpndoc

Pages exports to .txt, .rtf, doc, .docx, pdf, .html, .epub and Pages '09 .pages. But not to compressed .html.

To my knowledge .chm files are not used on Macs (and are deprecated on Windows), so are you looking for software to create them for Windows?

https://www.macupdate.com/app/mac/28171/ichmis a free .chm reader.

http://docbook.sourceforge.net/ exports to .chm amongst other formats.

http://aurigadoc.sourceforge.net/is another possibility.

http://www.helpblocks.com/is cross platform.

https://www.macupdate.com/app/mac/23919/simple-help-editor may be suitable but has not had an update in a while.

If you want to create more usable .pdf and .epub Help files you can do that from most Mac Apps. I use Pages '09 because of its more advanced features to create Manuals distributed as .pdfs.

Outlining, non-contiguous text and object selection, insertable multiple captured pages, high res previews of templates, ability to organise custom templates into folders, ability to preview multiple pages of templates, auto resizing of inserted graphics, cmyk colors that stick, more direct application of style properties via Toolbar, partial controlled application of Character Style overrides, ability to apply Character Styles as part of search and replace, Sidebar Glossary with links, selective importing of Style sets, rotatable tables and charts, copy and pasting of pages across documents, copying of selections and conversion to vector pdfs via Preview, links to other Pages documents, combined Paragraph and List Styles, highly automated, range of free Endnoting/Footnoting add-ons, detailed and reliable List Styling, faster, more efficient, compatible, and reliable (less likely to lose all your work) are just a few off the top of my head.