Google Talk

Description

Homepage	http://www.google.com/talk/
Type	XMPP-based, proprietary
Identity	Jabber ID (JID), e.g. usr@a.b.c/home with "home" being a "resource", which distinguishes the same user when logged in from multiple locations (simultaneously)
Interoperability	XMPP, LiveJournal, Gizmo, AIM

To add someone using AIM to your GTalk account, add <screenname>@aol.com. If their screen name is an email, add <username>(<domain>)@aol.com. For example, to add bob@me.com use bob(me.com)@aol.com. Note that if your GTalk address and AIM screen name are the same, messages from your AIM contacts will be received by both.

Apart from using and being compatible with XMPP, Google Talk also has proprietary elements.

Note that "a Gmail account is required to use Google Talk or other download clients" (says Google).