If you create a lot of add-ins by zipping up a source folder and changing the file extension to jmpaddin, you might find this add-in to be very useful. If you do not know what I mean by creating an add-in this way, check out Jeff Perkinson's Blog post about this method.
Basically, this add-in very quickly does the process of zipping up your add-in source files into a JMP Addin (.jmpaddin) file. There is the ability to save the information about an add-in so that you can easily build any add-in later on.
I find this to be extremely useful when I need to make incremental changes to an add-in. It allows you to quickly take a change that you made in your source files and easily test that change as an installed add-in.
Custom Add-in Builder Screenshot
This add-in does not delete or move any of your files except that, when building an add-in, it will overwrite your .jmpaddin file, if it already exists.
See the attached PDFs to see how it works and how you can get started using the add-in.