Need a to-do list app manager for your Android phone? Google Keep is the best. Easy to use, lightweight (not a crushing number of features), and very likely to be used.
Secrecy has its charms. This app, Cloak, uses Instagram and Foursquare location data to find where others are. Reminds me the map in Harry Potter. Avoid that professor whose class you have missed. Of course all bet are off if they are not on any of the more popular social locations services.