Boom 2 - Boom is a simple volume booster that lets you boost the volume of your Mac and your music files.
FxSound - Clearer Sound for Your PC. The new FxSound boosts your sound quality, volume, clarity and bass.
Boom 3D - Audio enhancer with 3D surround sound
Equalizer APO - A system-wide equalizer for Windows 7 / 8 / 8.1 / 10 with channel remapping/copying capabilities
eqMac 2 - The open-source macOS audio optimizer 🎛️
Letasoft Sound Booster - Boosts sound volume above maximum level