's instant messaging protocol
standing for O
ystem for C
ommunication in R
ealtime. Despite its name, the specifications for the protocol are proprietary
. AOL has to gone to great lengths to keep competitors, namely Microsoft
and Cerulean Studios
, from implementing compatible clients for their proprietary messaging system.
Currently OSCAR is in use for AOL's two main instant messenging systems: ICQ and AIM. Large parts of the protocol are nowadays understood after reverse-engineering the protocol, implemented by an ever-increasing number of clients.