Here's a partial list of social networks I've been a part of:

EFnet
Undernet
DALnet
usenet
AOL
ICQ
Geocities
Angelfire
Tripod
Xoom
Plastic.com
Friendster
Myspace
FriendFeed
SixDegrees
LiveJournal
Flickr
Yahoo Groups
reddit.com
del.icio.us
Tumblr
Facebook
Discourse
Google+
Google Wave
Google Groups
Orkut
LinkedIn
Instagram
Twitter
Discord
Slack

Just a reminder: this is not an end. This is not a beginning. This is a middle. There will be more.