Except for resources provided through the HomeSeer internal package (Scheduler.DLL) and the communications framework (HSCF.DLL) everything needed to create a plugin can be found in this SDK.
What is a plugin?
A plugin is an add-on component, or extension, to HomeSeer that provides additional functionality to the system. It is an executable application that runs in the background on a HomeSeer controller or remotely on another computer.
Plugins are made up of an executable file that acts as the primary integration point for HomeSeer and HTML files registered as feature pages.