Here are 7 Hidden features of OS X Yosemite. See iOS 8 Hidden Features also.
Yosemite now is having a Dark Mode for when you are working late at the night. Just head to the System Preferences >> General and then click on “Use dark menu bar and Dock” button from there. Both will go to dark and will be alittle easier on your eyes.
2. SHARE YOUR SCREEN FROM MESSAGES:
Screen sharing is even easier in the Yosemite. If both the users have Messages then you can click the ‘Details’ button and click on the screen sharing icon to share your screen with someone. This can do make tech support alittle easier for users.