Speaker Booster manages your mobile's audio levels and increases them to produce a stronger sound.
The app divides your mobile's audio into three different categories: System, Media, and Notifications.
System handles the volume of your calls. Media takes care of games, videos, and music. Notifications are self-explanatory.
Unfortunately, it's a little too simplistic and you can't manage individual apps. Speaker Booster works very well and can be used with headphones or speakers.