MicSwitch is described as '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!)'. There are six alternatives to MicSwitch for Mac and Windows. The best alternative is AHK MicMute, which is both free and Open Source. Other great apps like MicSwitch are Shush (Paid), Mic Drop (Paid), MuteMyMic (Free) and Talk Toggle (Paid).
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).