Voiceover

Yes, Voiceover is an OSX application, but I think this one is important enough for it’s own category!

I’ve written a quick guide to Voiceover basics, as I’ve found the official documentation too long winded.

The best place for up to date documentation is the community created Macpedia.

Greg Kearney has created a database of VO accessible applications: The VoiceOver compatibility list.

Apple do a more detailed technical overview of creating accessible applications in Cocoa.