Recently, one of the my go to sites for all my simple GNSS questions had severe reoccurring downtime. Out of concern they were considering taking down the website, I decide to archive their entire website for offline use. I found the software, HTTrack, that worked really well. It was impossible to distinguish between the online site and offline (HTTrack generated) site.
" It allows you to download a World Wide Web site from the Internet to a local directory, building recursively all directories, getting HTML, images, and other files from the server to your computer. HTTrack arranges the original site's relative link-structure. Simply open a page of the "mirrored" website in your browser, and you can browse the site from link to link, as if you were viewing it online. HTTrack can also update an existing mirrored site, and resume interrupted downloads. HTTrack is fully configurable, and has an integrated help system."