A JMP add-in is a JSL script that you can run anytime from the JMP Add-Ins menu. You can create submenus to group your JMP add-ins and have many levels of menus, if desired.
Experienced JSL script writers can create scripts that extend JMP in many ways (for example, add a custom analytical tool or a user interface to communicate with a database). The JMP add-in architecture simplifies deploying and using these complicated scripts.
You can send co-workers a suite of scripts and tell them how to run them. Another option is sending a single add-in file that any JMP user can install and then use just like any other part of JMP.
As a JMP user, you might be given add-ins to use by co-workers. You can also find add-ins on the JMP website at https://www.jmp.com/addins.