Mac: Worried that an app might be using your microphone or webcam without your knowledge? Micro Snitch monitors your mic and camera so you know if anything weird's going on.
Micro Snitch is made by the same developers as Little Snitch, which monitors your network for connection attempts. Micro Snitch does a similar thing, but instead tracks when an app attempts to use your microphone or camera. It's probably not something most of us ever need, but it's nice to know it's there if you ever do. You can check out a free trial on the developer's site if you want to test it out.