Equalizer APO - A system-wide equalizer for Windows 7 / 8 / 8.1 / 10 with channel remapping/copying capabilities
FxSound - Clearer Sound for Your PC. The new FxSound boosts your sound quality, volume, clarity and bass.
DFX Audio Enhancer - Formerly known as DFX Audio Enhancer, FxSound Enhancer instantly boosts the sound quality of the music on your PC.
Boom 3D - Audio enhancer with 3D surround sound
Equalizer Pie - Equalizer Pie is a free audio manipulation application for OS X.
Boom 2 - Boom is a simple volume booster that lets you boost the volume of your Mac and your music files.