Other major plugin types

All major plugin types are described in the Moodle documentation at https://docs.moodle.org/dev/Plugin_types. For completeness, they are listed here:

This is clearly a long list, and this book isn't going to be able to delve into the details of every one. Again, if you are faced with a seemingly complex Moodle customization, then the first step is to determine which plugin type will best provide the change to Moodle you require.