Mac: Debug menus are great little secrets that often hide useful extra settings. Apple's hidden these menus in its default software for a while, and it's often easy to unlock with a Terminal command.
To enable these debug menus, just open up Terminal (Applications > Utilities), type in one of the commands listed below then press Enter. Not every Apple app has these, but we've tested each of these and they all work on macOS Sierra. If you have the application open, you'll need to close it and reopen it before you see the new menu.
Adds option to manually refresh your list (and other options you'll probably never need).
defaults write com.apple.reminders RemindersDebugMenu -boolean true
Mac App Store
Adds in options to delete cookies, reset the app and hide pre-release software.
defaults write com.apple.appstore ShowDebugMenu -bool true
Adds a ton of options, including stress testing and logging.
defaults write com.apple.Safari IncludeInternalDebugMenu 1
Adds a variety of odd printing options and Time Machine backup access if you need an older version of a contact.
defaults write com.apple.AddressBook ABShowDebugMenu -bool true
Allows you to change the number of weeks and months in certain views and clear out the cache.
defaults write com.apple.Calendar ABShowDebugMenu -bool true
Most of us don't really ever need these special debug menus, but it's always nice to know they're there, and occasionally they come in pretty handy.