Mac OS X
VoiceOver was first introduced in Mac OS X 10.4 and the target was users who had difficulty in reading due to vision impairment, particularly the blind. A preview had also been made available for Mac OS X 10.3 Panther, and was titled "Spoken Interface Preview."
VoiceOver treats the user interface as a hierarchy of elements, which are navigated by various keystrokes. Elements also are "interacted" with - for example, interacting with a text box allows reading its text and, if possible, editing it; interacting with a scroll bar allows it to be moved using the keyboard.
VoiceOver also includes support for many Braille displays for those who are both blind and deaf. In addition, VoiceOver includes features for those that cannot use the mouse, such as keyboard based navigation.
For users with MacBooks or Magic Trackpads, a number of special multitouch features are also available. The trackpad will respond to gestures, much like iOS's version of VoiceOver. A specific example is using the trackpad to explore the actual visual layout of elements on the screen - sliding one's finger around the trackpad will activate elements.
In Mac OS X 10.5, Apple added the "Alex" voice, which offered improved quality of speech and a more human-like sound. Previously, the voices were directly descended from those used in Apple's "Speech Manager", which originated in the early 1990s.
In Mac OS X 10.7, Apple offered the download of RealSpeak voices from Nuance for use with VoiceOver.
Read more about this topic: VoiceOver