See eWriter eBooks for more details on the benefits of the eWriter format.
If you are going to deploy eWriter help files for your own software documentation you need to install the eViewer.exe executable along with your application and consider some issues regarding making your calls to your files and choosing the best file extensions. Please see EWriter for Software Help in the reference section for details on this.
On Windows 10 users are automatically prompted to get the eWriter Viewer from the Windows Store when they try to open an .ewriter file. A downloadable installer for the Win32 version is available for users on older versions of Windows. See The eWriter Viewer App for details.