I mean, you had your friends page, which aggregated all the posts from people you'd added as friends (this was a one-way thing, it didn't require the other person's agreement). You could also make posts locked so that only your friends, or specific subsets, could see them. (Later it became possible to separate these two different functions of adding someone as a friend, although a little troublesome. On Dreamwidth these are entirely separate functions, with the "friends page" now called the "reading page"; you "subscribe" to people to add them there, and you "give access" to people to let them read your locked posts.) People can also set up "communities" that people can join and post to. And of course people had profiles where they could write a little bit about themselves, and you could see their friend lists (or these days on Dreamwidth, subscription lists and access lists).

Seems to me it basically resembles the later "social networking" sites in features (and outdoes them except possibly Google+), just the tone was more focused on long-form blogging.

I guess the one thing lacking that people these days would expect was that you couldn't easily upload pictures and such (that was a paid feature IIRC; haven't checked how that works on Dreamwidth). But if you ignore that...