Composer is a super useful tool in modern PHP, and there are times you want to make packages that you will use in many other projects. I often see people development within their applications, meaning they create their models, views, commands, events and more in the app folder of their applications...then when they want to make a package, they have to copy all those files, update the namespaces, and test that it all works.
But there is a much easier way. I put this video together to help explain how to set it up:
Here is a gist, which includes the important parts in order to allow Composer to use the local package for development: