I always have a Reddit client on my phone so I can waste some time with the extensive articles and amusing comments on Reddit. There are many Reddit clients and this just happens to be the one I've used for a while.
This allows you to remotely manage your Android device from your computer. Its amazing all the features and the ability to see what your phone's camera sees is very fun and useful. It also has full tracking abilities.
The easiest and best music creation package I have ever used on the Android platform. This has so many synths built-in, including a vocoder and an excellent drum machine. I use FL Studio on my desktop, but this beats the mobile version of FL Studio...
This app will backup and restore (hence the name) all your SMS. Not only can you schedule a backup to happen automatically, but also have that backup sent to your Google Drive. Its saved me so much trouble many times.