Windows OS X is a family of operating systems developed by Apple for it's iOS products. A lot of people reported that their Macbook Airs are back to 0 from 1 after upgrading to Yosemite, and this is still not fixed in 10.10.1.
This is only for 3rd party apps, not for default ones, like Mail. Also, you cannot sign in another user with the main OS, that is, you can't use it for sharing your account. So it's not for personal use.
Additions to OS X include Advanced Power Management for the program interface, which reduces power consumption when inactive, an Application notarization service for apps that authenticate or quickly verify source code, and full hardware support for 802.11ac MIMO (multiple in/multiple out) Wi-Fi, including support for Wi-Fi 6. There are new Messages features that help you stay in touch with friends and family, like pinning and grouping conversations. Advanced FaceTime features provide direct, consistent calls and chats between FaceTime users, even if they're on different Apple hardware. d2c66b5586