Here is a list of all documented files with brief descriptions:

doc.h
kdb.hpp
kdbcontext.hpp
kdbexcept.hpp
kdbextension.h	Extension functionality
kdbhelper.h	Helper for memory management
kdbinternal.h	Includes most internal header files
kdbio.hpp
kdbmeta.h	Metadata functions
kdbmodule.h
kdbobsolete.h	Obsolete/Deprecated API
kdbos.h	Operating system specific workarounds
kdbplugin.h	Methods for plugin programing
kdbplugin.hpp	Helpers for creating plugins
kdbprivate.h	Private declarations
kdbproposal.h	Proposed declarations
kdbthread.hpp
kdbtimer.hpp
kdbtypes.h	Elektra's data types for C and C++11
kdbvalue.hpp
key.hpp
keyexcept.hpp
keyio.hpp
keyset.hpp
keysetio.hpp
markdownlinkconverter.c