What accessibility features does mac OS have and how do I enable them?

Apple includes assistive technology in its operating systems as standard features.  The accessibility features can be found in most iPhone, iPad, iPod, and Mac OS X devices.

Mac & iOS Accessibility Resources

• Mac OS Accessibility (all Apple devices)
• Voice Commands on Mac
• Dictate messages and documents on Mac
• Commands for dictating text on Mac
• Accessibility Reader (listen to or change how text appears)
• Change Read & Speak settings for accessibility on Mac
• Mac OS Accessibility Shortcuts
• Mac OS X Keyboard Shortcuts
• iPad Accessibility Features
• iPhone Accessibility