Scret - Perguntas Anonima
The Scret: perguntas anonima app was very popular just a few months ago. It allowed users to ask questions anonymously to others. It allowed users to post anonymous messages in a similar fashion to Instagram. Users could also sync their accounts with their social networks. There are both an iOS and Android version and a basic web version. If you're looking for a good alternative to the Secret app, try App Kiwi or Swarm.
Scret: Despite the name, this question-answer app is actually a social networking service. Users can send and receive questions from friends. However, if you don't want to reveal your identity, don't bother using it. In fact, you're not required to use the app to communicate with other people. All you need to do is send a question and wait for the answer in a new story.