Trick question. It's not a thing. It's this guy:
Basically, he wears a top hat, lives in your computer, and waits for you to tell him what kind of application you wish to create.
Not every new computer comes with a Yeoman pre-installed. He lives in the npm package repository. You only have to ask for him once, then he packs up and moves into your hard drive. Make sure you clean up, he likes new and shiny things.
$ npm install -g yo
Yeoman travels light. He didn't pack any generators when he moved in. You can think of a generator like a plug-in. You get to choose what type of application you wish to create, such as a Backbone application or even a Chrome extension.
To install generator-ngal from npm, run:
$ npm install -g generator-ngal
$yo ngal Name
Creates a complete module named Name, the below commands will allow you to generate single sections of code.
$yo ngal:config Name
$yo ngal:controller Name
$yo ngal:directive Name
$yo ngal:main Name
$yo ngal:service Name
$yo ngal:version Name