Back in the days when the web was just Flash, it wasn't as easy as Ctrl+S to save content you wanted to keep. In a few years, you may need to spin a VM with an older OS to launch a flash-able browser. (https://en.wikipedia.org/wiki/Adobe_Flash#End_of_life)
I wonder if it's easier with java applets.
I had to jump through hoops to get an applet I wrote only 10 years ago running.
I personally prefer mhtml, though with the recent breakage with firefox, I've been doing PDF.
Archiving something interactive.. that's a different story.
- "one that benefits everyone": probably wikipedia+scihub, but I think you would have already guessed that. A knowledge database that benefits everyone looks a lot like the internet, minus the serving issues. So probably something closer to ipfs.