"Add-on": is wordpress plugin , you can install like as normal wordpress plugins.
"Integrate add-on": is wordpress plugin , have no real function, their function is make a bridge to make openpos work with Parent plugin. The parent plugin listed on add-on description.
"License: Free": free for openpos customer with purchase code.
"License: Support Service": free for openpos customer with support service non expired.
Addons are Free resource we have done. Addon NO relationship to Openpos license. This is independent, It mean once you buy openpos, you have support on openpos features only. YOU HAVE NO SUPPORT FOR ADDON.