We always had a wiki page on how to create your own Horde module. The steps outlined there allow you to get started quickly.
There was no specific reason though why those steps could not be automated. Based on the core script presented on the aforementioned wiki page I created a complete script that allows you to initiate a new Horde module with a single command.
framework/devtools/horde-generate-module.php fancy "Gunnar Wrobel <firstname.lastname@example.org>"
The line above will create the stub for the new Horde application Fancy.
Once you created the new module this way you still need to register the new application in the Horde registry. This can be done within the directory config/registry.d. For details see the README file in that directory.
In addition you can set an icon that should represent your module. Refer to the instructions on the wiki page for that.