In the book Developing Mobile Games with Moai SDK is referred to the AKU, the interface between host and framework. Also in some of the code AKU is included.
But no AKU files can be found in the source code at all. Is this a part that is currently worked on or has been deprecated in the development branch? Unfortunately the release versions can't be downloaded anymore because they still link to the shut down moai cloud.
After the book was released, Moai SDK suffered a major reorganization to be a little bit more modular.
All the AKU stuff was moved to "host.cpp" files across modules. For example in moai-core, you'll find a host.cpp file that includes several AKU methods.
Besides this, you can also clone the Version-1.4p0 tag, that is the one I've used for the book.
Hope this works for you!