I understand that app groups offer the abilities for apps to share data such as NSUserdefaults across two applications. If I'm misunderstanding app groups then please correct me. If not, then what is the best way of finding third party companies that offer their app groups up for grabs to share user data?
Yes , app groups used to share data between app/s & extensions , there is no sharing ability between apps from different developer accounts only from the same account so the other proposal is not even possible