There is a good enough web app for Q2A by Kai for Android. You can search in Android posts. For native android/ios app I don't think there exist a great app. I have made the app by Noah work- it does the purpose though not all features are there. If interested you can try the app - gateoverflow from play store. Before using you need to register at http://gateoverflow.in
. This app you can make from the available code given in some 30 mins.