ICQ was nice but everyone moved on to Yahoo Messenger. That was the bomb. Truly unbelievable Yahoo didn't capitalize on that. Everyone used it.
after ICQ, from what I remember AOL Messenger was the dominant force in the US, MSN was very popular in many countries, but across Asia, Middle East, and many Eastern European countries, Yahoo Messenger was the de facto standard.
Not dissimilar to the situation we have today with WhatsApp and WeChat and iMessage. Except back then you could use pidgin or trillian as multi protocol clients which solved the issue. Somehow, we have regressed so much in this area in the last 20 years.
I personnally didn't even knew there was a Yahoo issued Messenger until this comment.