Best Free Microphone Booster Software

Audacity

It offers a dedicated Recording Volume slider to increase or decrease the microphone recording boost

Expstudio Audio Editor

Use it to record audio and boost the volume of recordings using its Playback section.

Equalizer APO

Use it to give the recording audio boost capability to all system audio recording tools. 

VOICEMEETER

Use it to boost the sound of two physical microphones and one  virtual sound source.

Mic Note

Use it to create Voice Notes and Text Notes with boosted audio input.

Tap on the below icon to know more about these software.