the barking pizza bbs (1996?)
diary-l mailing list (1997?)
little bastard webring (1998?)
metafilter (2001)
diaryland (2001?)
livejournal (2002)
friendster (2003?)
myspace (2005?)
facebook (2005-)
twitter (2009-)
mastodon? (2022-)
cohost? (2022-)
I have to guess for a lot of these because there's little to no trace of them on Today's Internet. The relative longevity of fb and twtr compared to the rest is interesting!