I added a new document to the MonoDevelop developers documentation page: API Overview.

The public MonoDevelop API is really extensive, and it is not easy for add-in developers to find out which part of the API they have to use to do certain operations. This document is basically a high level description of all functionality provided by the API, with information about which classes and objects provide that functionality. The document doesn't give much detail about how to use the API, this will come in separate feature-specific documents.

I hope you find it useful.