Back in the nineties the web was fairly new and people still used a thing called usenet quite a bit. You interacted with it kind of like email (Google groups is

Back in the nineties the web was fairly new and people still used a thing called usenet quite a bit. You interacted with it kind of like email (Google groups is actually the final vestiges of it) - and the go offline button would just download all your emails and newsgroups and you got peruse them offline at your pleasure. It might seem strange also that back in those days you downloaded your emails from a server using POP3 rather than looking at them remotely (e.g. Web or IMAP), and you viewed them offline.