Paint or write slight messages on places where you are. Tag them all! What kind of character are you?
Other users with the app can see your messages too, but you are completely anonymous without any further logins or something. You can even use this when you are offline. :)
Use this for geocaching or leave a scribbling or text message to strangers.
You can set up a widget on your phone desktop which shows the nearest comment on your current location.
This app needs a strong gps signal for localization.
If there are really bad messages feel free to ask me for a removal. You can do this with my twitter account http://twitter.com/can_tag or email.