MSN Messenger, Angelfire, Geocities, marquee tags, flame gifs.
And forums, of course. Music forums, mostly. The dopamine hit when you posted enough to achieve the next "rank". Scrolling flame text in your signature.
I was 9 and had a cringy fan website for my favourite band. I used it to practice HTML and JavaScript (which blew my mind). HTML frames were the subject of a holy war at the time, so I had separate versions of the homepage, one using frames and one without. I would spam the (very few) visitors to my site with alerts and prompts.
Every now and again I would get random emails from (real) people around the world asking me to check out their band or their website etc. And most of the time they were actually good (by my standards at the time).
There was also, of course, the dreaded click which indicated your connection had been lost, most probably because someone had picked up the phone. So you'd have to reconnect and listen to that screechy dial-up sound.