Get the acronym out of the way early doors....
• Web Accessibility Initiative.
• Accessible Rich Internet Applications.
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• It’s at ‘Final Call’ draft stage, i.e. it’s not a formal specification (yet).
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WAI is the ‘branch’ of W3C that develops accessibility standards guidelines.

In addition to WAI-ARIA, WAI are also responsible for WCAG (which I’m sure you’ve all at least heard of), plus some others that you might not have, e.g. ATAG (authoring tool) & UAAG (user agent).