Text-to-speech, or speech synthesis, has been around for a long, long time. Every Mac, since the very first one, has had speech synthesis built right in.
To get a sense of this, bring up Terminal (it’s in Applications > Utilities) and type:
say “I read the Loop every day, and now my teeth are the color of the winter sun”
Hit return, and you’ll hear your Mac’s computer voice, in all its default glory. Now open System Preferences and select the Dictation & Speech icon. Fiddle with some of those options and click the Play button to try them out. Now if you go back to Terminal, your new settings will be reflected when you ask it to say something.
Now that you see what comes built in, click the headline link and give this demo a try. There’s something about having an avatar, and the quality of the voices are great. Remember, no curse words. Oh, OK, go ahead. So much fun!