There are lots of APIs when it comes to Microsoft OCS 2007. Anyone knows what is the API behind an application like Live Meeting? UCMA 2.0?
Live meeting doesn't use UCMA 2.0 - it has its own APIs (two of them, in fact) - see here for an overview, and here for the reference documentation for the service API (the main API for interacting with LiveMeeting)
You're right - there are a crazy amount of APIs for OCS development - see here for an overview of each.