The library was developed to implement Material Design for the new Angular. It's still a work in progress, but it continues to evolve. There are, however, enough components in place for it to be adopted already. You should know that it is still in Beta, so a certain amount of caution is good if you consider adopting it. The official documentation can be found at https://material.angular.io and the repository can be found at https://github.com/angular/material2. It is a quite popular library with 10,000+ stars. 

Angular Material promotes itself with the following bullet points:

• Sprint from zero to app: The intention is to make it very easy for you as an app developer to hit the ground running. The goal is for there to be a minimum amount of effort in setting it up.
• Fast and consistent: This is to say that performance has been a major focus point and also that it is guaranteed to work well on all major browsers.
• Versatile: This puts focus on two major points, there should be a multitude of themes that should be easy to customize and there is also great support for localization and internationalization.
• Optimized for Angular: The very fact that it is built by the Angular team itself means the support for Angular is a big priority.

The framework consists of the following parts:

• Components: This means that there are a ton of constructs in place to help you be successful, such as different kinds of input, buttons, layout, navigation, modals, and different ways to show tabular data.
• Themes: The library comes with themes preinstalled, but it's also easy to refer to external themes. There is also a theming guide, if you have your heart set on creating a custom theme, at https://material.angular.io/guide/theming.
• Icons: Material Design comes with over 900 icons so you are likely to find just the icon you need. For a full display of what those are, go to https://material.io/icons/.
• Gestures: Not everything in a UI is a button click. As Material Design supports mobile, it thereby supports mobile gestures through the use of the library HammerJs.