OSX status bar application that mutes microphone until fn is pressed.
Icon will turn orange when microphone is not muted.
Double press fn or use a menu by clicking on the icon to reverse the behaviour.
I did not sign the App. To enable exception for this app follow https://support.apple.com/kb/PH11436?locale=en_US
If you want to be sure, just compile the project, Archive & export PushToTalk.app