It was proprietary client software released in 1996 and bought by AOL two years later.
It relies on a service operated by a single party, which is now sunsetting it.
According to the Wikipedia article, when ICQ was under AOL's stewardship, "AOL pursued an aggressive policy regarding alternative ("unauthorized") ICQ clients."
The article details all the tactics that AOL implemented in the service to break unofficial clients.
I don't see where the word "democratic" connects with ICQ.