DarkAudacity - DarkAudacity is a build/fork of Audacity with quote "a darker more modern theme - and a few small tweaks."
Audacity - Audacity is a free and open-source audio production software suite that includes a surprising array of editing tools and recording systems.
Noise Destroyer - Remove Backround Noise From Audio or Video
Tenacity - Tenacity is an easy-to-use, privacy-friendly, FLOSS, cross-platform multi-track audio editor/recorder for Windows, macOS, Linux and other operating systems.
Adobe Audition - Mix, edit, and create audio content in Adobe Audition CC with a comprehensive toolset that includes multitrack, waveform, and spectral display.
GTK Wave Cleaner - GTK Wave Cleaner is a GUI application to remove noise (hiss, pops and clicks) from audio files in WAV and similar formats.