Was pleasantly surprised to see the beta of the new Lightning Component library being included in the Winter ’18 release. Quoting from the release notes (see page 533):
Find components more easily with the searchable component library. Preview the look and feel of components with interactive examples. To explore the new component library, go to https://<myDomain>.lightning.force.com/componentReference/suite.app where myDomain is the name of your custom Salesforce domain. You can also continue to use /auradocs/reference.app in your org. And the Component Reference section in the Lightning Components Developer Guide continues to be available to you. …snip… Let’s look at some of the highlights. Gone are the days when you had to imagine how a Lightning component renders and behaves in your browser. Many components now have interactive examples and source code for common patterns. You can also learn about how a component is used through a list of examples.
The component library is really for the built in base components what the auradocs at /auradocs/reference.app is for your custom components and with the additional of all the new base components in Winter ’18 this is a nice addition.