In a normal development situation, if the custom tools that we will create are meant to be something reusable, the best decision is to deal with them as independent projects. Let's do this with the AppBuilder tool.
First, create a new Unity project with the name AppBuilder
and then move the files related to this tool from the Run & Jump project here.
Your project must look like this:

We used this folder structure here just to match it to the structure we have in Run & Jump. However, as a good practice, always use a root folder with the name of the tool you want to share, if possible.