LiveJournal
LiveJournal was one of the first ever sites that allowed people to write about their day. Whilst a few other sites came first, LiveJournal's popularity was 100s of times more popular than the other sites. As LiveJournal reached the peak of its popularity, however, a new site, Blogger, had been created and soon overtook it in popularity. Since that time, MySpace and other similar sites have easily overtaken Live Journal in popularity.
Live Journal nonetheless was a cultural phenomenon at its time. LJ Drama was the main opponent of LiveJournal.
The founder of LiveJournal, Brad Fitzpatrick, now works for Google.