MSN Messenger
The nudge, the buzz, and a status message full of song lyrics.
Where an entire generation did its socialising between four o'clock and bedtime, in front of the family computer.
Signing in and out repeatedly so a specific person would notice you were online is a documented behaviour of the era and everybody did it.
Personal messages were passive-aggressive song lyrics. The nudge shook the whole window and was, correctly, considered rude.
Cost back then
Free, but you paid for the phone line
Goes for now
Gone; the nudge sound lives on as a meme