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

• Speech-to-Text Quick Sheet (Mac OS)
• Text-to-Speech Quick Sheet (Mac OS)
• Mac OS X Accessibility
• Mac OS Accessibility Shortcuts
• Mac OS X Keyboard Shortcuts
• iPad/iPhone Accessibility Features
• Video: How to add accessibility features to the MAC Control Center