ICQ

ICQ is a cross-platform instant messaging and VoIP client. The name ICQ derives from the English phrase "I Seek You". Originally developed by the Israeli company Mirabilis in 1996, the client was bought by AOL in 1998, and then by Mail.Ru Group in 2010.
The ICQ client application and service were initially released in November 1996, freely available to download. ICQ was among the first stand-alone instant messenger (IM)—while real-time chat was not in itself new (Internet Relay Chat (IRC) being the most common platform at the time), the concept of a fully centralized service with individual user accounts focused on one-on-one conversations set the blueprint for later instant messaging services like AIM, and its influence is seen in modern social media applications. ICQ became the first widely adopted IM platform.
At its peak around 2001, ICQ had more than 100 million accounts registered. At the time of the Mail.Ru acquisition in 2010, there were around 42 million daily users. Since 2013, ICQ has 11 million monthly users.