Slashdot and Segfault.
At the time, all my online friends used it to discuss techie things.
First social network with real people in my local area? Whirlpool.net.au
It started as a site for peer support for one ISP but became a forum for local and regional technological issues.
There were also other niche forums for niche interests, including a Nissan Pulsar forum; we would organise cruises IRL and share technical information.
Most of these communities have been subsumed by Meta, which I believe is a terrible thing. Their platforms are not as conducive for that sort of socialising, without significant amounts of friction.