Friends Monitor app for iPhone and iPad
Developer: Lorenzo Sfarra
First release : 31 May 2014
App size: 1.9 Mb
IMPORTANT - PLEASE READ BEFORE DOWNLOAD: since 30th April, 2015 Facebook changed its APIs and the behavior of the app has changed: an app can now only get the list of friends *also using the app*. Facebook confirmed that this behavior is "by design" and prepared a FAQ about it: https://developers.facebook.com/docs/apps/faq#friends_list .
The Friends Monitor main aim is to notify you when your Facebook friends become available to chat and collect this type of information to create statistics. You can select the friends you want to monitor.
No data will be published on Facebook or notified to the monitored friends.
A system of daily, weekly, monthly graphs will show you the way in which your friends are available on Facebook.