Take note of the "Post Processing Tool" attribute in a form builder's properties. We can see that it is listing down a list of Process Tool plugin for app desginer to choose.
We can trace this behavior to the property defintion file "form.json" - https://github.com/jogetworkflow/jw-community/blob/6.0-SNAPSHOT/wflow-core/src/main/resources/properties/form/form.json#L81
This is the excerpt of the file that is responsible to generate such dropdown selection.
form.json
{
name: 'postProcessor',
label:'@@form.form.postProcessor@@',
type:'elementselect',
options_ajax:'[CONTEXT_PATH]/web/property/json/getElements?classname=org.joget.plugin.base.ApplicationPlugin',
url:'[CONTEXT_PATH]/web/property/json[APP_PATH]/getPropertyOptions',
default_property_values_url: '[CONTEXT_PATH]/web/property/json[APP_PATH]/getDefaultProperties'
}