Can anyone recommend a good app for processing who has followed/unfollowed me while I was away?
no such thing, that state is lost, any app can only report on changes since you signed up with it
You can add location information to your Tweets, such as your city or precise location, from the web and via third-party applications. You always have the option to delete your Tweet location history. Learn more
no such thing, that state is lost, any app can only report on changes since you signed up with it