For those of you who are confused by this app or why it seems to be popular at the moment:
Apps with this concept tend to pop up every few years (Honesty Box, Ask.fm, Formspring, etc.) and be intriguing to younger generations, but die out rather quickly due to the cyclical nature of said concept. Basically, the idea of "Oh, hey, my fellow high school/college students and I can say some anonymous things to each other!" is interesting, so people in that generation jump on it hard for a few days/weeks.
The reason they seem to die out just as quickly as they rose to prominence is that, well, there's only so much you really want to say anonymously to your friends (if anything). After a week or so, people run out of messages to send, and the community grinds to a halt.
Thus, the app dies, and a few years later another person introduces the app again, and the process starts over.
Being cynical and annoyed by this is up to you, but it's a pretty natural cycle based on how online social interaction trends tend to work; it's a trend that will likely continue in bursts for the foreseeable future.