An AppBuilder plugin is a standalone javascript package. Plugins are added to a Tenant, and then individual user within the tenant will be able to use the plugin given they have the permission.
Plugins should be added to /assets/. Plugins common to all tenants (like the ABDesigner) should go into /assets/default. Plugins for a given tenant should be added to a folder with the tenant’s id (assets/tenants/${tenant_id}).
Plugins need to export a function that accepts the ABFactory as a variable.