@blogdiva@mastodon.social My first was the dialup service Prodigy in 90 or 91, which I believe used its own protocol (it definitely used its own image formats). Technically only a small slice of it was the internet (just email, iirc), but I used that bit, so it counts.
I remember being envious of CompuServe users because they had the "cb simulator" (early text-only chatrooms).
There was a brief period in the 90s where having a 7-letter last name was, well, not "cool", exactly, but maybe "convenient in a neat way". So many usernames had a technical cap at 8 characters and "first initial last name" was such a common way for organizations to assign usernames.