AHK MicMute is described as 'open-source program that allows you to mute your microphone with a pre-defined hotkey. It supports custom mute sounds, profiles, push-to-talk, AFK timeout, and more'. There are six alternatives to AHK MicMute for Mac and Windows. The best alternative is Shush. It's not free, so if you're looking for a free alternative, you could try MuteMyMic or MicSwitch. Other great apps like AHK MicMute are Mic Drop (Paid), Mutify (Paid) and Talk Toggle (Paid).
MicSwitch allows you to mute/unmute your system microphone using a predefined system-wide hotkey which will affect any program that uses the microphone (no more heavy breathing during Skype conferences, hooray!).
Quickly mute and unmute your microphone through a user-configurable hot key. Keep your voice chats crystal clear and free of noise. Fully configurable - Customize any hot key of your choice (supports both keyboard and mouse button combinations).