Backwards is now discontinued.
With the popularity of Apple Music and iTunes Match, people don't own the license to their music anymore, and in these cases, iOS will block access to the files. Unfortunately, having access to the files was vital for this app. With the songs blocked, it gave the impression that the app did not work, even though it was not the case. There's not much to be done. That's why it was removed from the AppStore.
Here is what the original app description was:
Play any song backwards.
Use this app to discover hidden messages in your music, whether the artist intended it or not. It's also interesting to hear how your favourite songs sound like in reverse.
Warning: Your songs need to be free of DRM (Digital Rights Management) or they will not be accessible to the app. Songs synced from your iTunes library should work, but songs synced through systems like iTunes Match and Apple Music may not.Features