The Dr Drums app is a free Android app focused on live drum pads playing. It has a total of 5 pre-installed drum kits that each have 16 sounds. You have volume control for each of these sounds, as well as a pan slider, for stereo speakers. After making your settings, you can save the drum pad settings and have them loaded later. You can have as much as 8 drum pad settings of this kind that you can access at any time. The app is best used on a large tablet screen, as the pads are really far away from one another. The app is rather basic, but also easy on your phone's or tablet's memory and works well on new and recent Android versions (2.3 and up). This is the only 4x4 drum machine I have seen so far and it is fit for percussionists that have worked with different drum sounds and tones and can get a great amount of diversity from this app. It is just sad that there are no settings to this app, as well as the fact that you cannot add sounds of your own. Even so, the sounds are great and do not have stupid short release time. That means that the Dr Drums app has great polyphony and can produce more realistic drum sounds.