For many years, there have been alternative AIM clients. Pidgin (formerly GAIM), Trillian, Miranda and others have all over the years worked to keep up with the official client and, more importantly, the AIM protocol. AOL has always encouraged people to use their official client, and used to be known for changing their protocol as to make it incompatible with these 3rd party clients. They changed their tune in late 2006, when they opened up the protocol to allow people to easily develop clients of their own.
Today, they’ve expanded that. AOL announced their Open AIM 2.0 developer program, the next step in giving developers an easy to use platform for AIM client and AIM plug-in development. The noteworthy step forward AOL is taking here is to allow tighter integration of an AIM client, so that it can be used in web applications and other such environments. While they have not given developers access to their true OSCAR protocol, they are still making moves.