HelpNDoc - What is HelpNDoc ? Easy to use yet powerful help authoring environment which can generate various documentation formats from a single source.
Wondershare PDFelement - All-in-one PDF editor
Dr.Explain - Dr.Explain software is a help file authoring tool.
Foxit PhantomPDF - Edit PDF files with our feature-rich PDF Editor. Download Foxit PDF Editor to convert, sign, scan / OCR & more. A speedy PDF Editor alternative to Adobe Acrobat.
CHM Editor - Best solution to edit CHM files
Google Docs - Create a new document and edit with others at the same time -- from your computer, phone or tablet. Get stuff done with or without an internet connection. Use Docs to edit Word files. Free from Google.