Speaker Booster Pro is a free Android app developed by Wait What that falls under the category of Multimedia and specifically Music & Radio. The app is designed to enhance the audio quality of your phone's built-in speaker by adjusting the frequencies to achieve a louder effect.

The app uses a loudness module that runs on devices with Android 4.4 and above, and all you need to do is tap the Boost button to get started. The demo song provided allows you to spot the difference and adjust the desired level of the effect. However, for older versions of Android, the slider must be used instead.

To get the maximum results, the app recommends using external speakers or headsets. It's important to note that listening to music too loud can cause damage to your ears, so use the app responsibly.

Overall, Speaker Booster Pro is a simple, easy-to-use app that can help enhance the audio quality of your Android device's built-in speaker.