Wikipedia
WallaMe
WallaMe is a free iOS and Android app that allows users to hide and share messages in the real world using augmented reality.
Users can take a picture of a surface around them and write, draw and add stickers and photos on them. Once the message (called Wall) is completed, it will be geolocalized and will remain visible through WallaMe's AR viewer by everyone passing by. A Wall can also be made private, thus becoming visible only to specific people.
All the Walls created worldwide can be seen in a feed similar to those of social networks like Facebook and Instagram, and can be liked, commented on, and shared outside the app.
WallaMe is mostly used to create digital graffiti and for proximity messaging.