"I found my tasks in the fruux app, but where are my calendars and contacts?"
The answer is quite simple: Right where they belong. In the native Android Calendar app and in the native Android Contacts app. The fruux app integrates with those, so you don't have to learn anything new and can just continue using the native Android apps. The only reason that our fruux app has an integrated task list feature is that Android has no native task list app (like e.g. Apple iOS has).