Some online software (i.e. certain Point-Of-Sale restaurant software) consists of web pages in a browser from an off-site URL/domain. But, when the internet fails, it has the ability to continue serving the pages and storing sales data for several hours at least. Then uploads the sales transactions and refreshes the web pages when the internet is fiannly restored.
I'm guessing the end user has downloaded a local *.exe program that can store copies of the web pages asked for, and serve them again to the browser when the web fails, storing data as well until able to upload it and refresh.
QUESTION: Do you know of ready-made software that gives a website this ability?