Has the term SIOPs (Standard Input Output Panels) been mentioned in regards to Group Chat and you wondered what they were only to find that an Internet search turns up links saying it isn’t supported? They were not supported when Group Chat released but added later and when the documentation was published the term SIOP was not used, instead
Microsoft Office Communications Server 2007 R2 Group Chat Add-ins API
As well there is some content on MSDN for Administering Group Chat Add-ins
So if you found yourself searching and frustrated, I hope that this helps you in that journey. By the way a Group Chat add-in is defined to be Web pages or Web applications that appear in the Group Chat client. The Add-ins appear in a panel, located directly beneath the chat input area.