Unveil hidden macOS (OS X) features
Mr.R 
When you press the power button on your Mac (installed with OS X Mavericks or Yosemite) your Mac falls into sleepmode. You can disable the power button’s directly sleep mode and have the ‘old’ shutdown dialog appearing instead, open OS X Terminal window and enter:
Disable the menu option: ‘Go ▸ Go to folder’ in the Mac OS X Finder menubar.
The OS X Dock is centered along the bottom of the screen, with OS X Terminal you can pin the Dock into the corner of your Mac’s screen. This method works with both 2D & 3D versions of the Dock.
If you don’t like the new notification center feature in Mac OS X 10.8, you can disable it (for all users on system level) with the following defaults write command.
When receiving e-mails containing HTML code in OS X Mail, you will notice that some e-mail messages comes with very small text. With this default write command it’s possible to set the minimum font size for text in HTML e-mails. In some cases changing the size of text will break the layout.
The ‘Simple Finder mode’ hides desktop files, and won’t let anyone open a new Finder window. Only applications in the Dock can be launched. Note that Spotlight can still be used for launching items. This command could be a nice alternative for setting up restrictions without a guest user account. Click Finder ▸ Run Full Finder, and then type in your admin password to start Finder in normal mode.
It’s possible to disable the rounded window corners while playing a movie in QuickTime, use the following command to disable them.