Oversight - Get notified when an app accesses your Mac's camera or mic

Radio Silence - Radio Silence is a network monitor and firewall for the macOS. The software stops apps from making network connections. The firewall runs in the background and does not require an open window.

Micro Snitch - Micro Snitch is an ultra-light menu bar application that operates inconspicuously. It helps figuring out if someone’s spying on you.

SpyBuster - SpyBuster is a free anti-spyware tool for macOS that helps to secure user data by detecting apps and websites that originate from or connect to servers in russia and belarus.

Little Snitch - Little Snitch is a firewall application that monitors and controls outbound internet traffic.

Tyke - Mac menu bar app that @torrez really needed to take notes