I came in at the tail end, but yes, LiveJournal. I spent most of 2007-08 spending way too much time on there while I lived in Japan and it changed my life.
Special shout-outs to early Dreamwidth, and Twitter back when you still had to send updates by text and you had your friends in your pocket.
Can I ask y’all a genuine question?
In all your life online, what’s the greatest social media you’ve ever used?