Greetings. I am looking for a reference to material that would help me develop plug-ins for Microsoft Office 2011 (OS X) applications. To begin, I am interested in developing a plug-in for Microsoft Word. Any pointers or references would be appreciated. Thanks in advance.
There’s no SDK to create plugins for MS Office 2011 
Is there an equivalent of MSOfficeAutomation.rbx that is cross-platform (not just Windows)?
No - there’s no SDK for MSOffice on other platforms so it can’t be MSOffice.
Writing a plugin for Open Office is, to be frank, painful.
And there’s no plugin SDK for Pages, Keynote, Numbers on OS X