Shush is described as 'Problem: Voice chat is awesome, but sooner or later you’ll send something you wish others hadn’t heard. Solution: Shush solves this problem by providing simple hotkey microphone management'. There are six alternatives to Shush for Mac and Windows. The best alternative is AHK MicMute, which is both free and Open Source. Other great apps like Shush are Mic Drop (Paid), MuteMyMic (Free), MicSwitch (Free, Open Source) 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).