As a build tool, we mainly use Webpack, but also have experience using Gulp and Grunt. With the release of Webpack 2, which has a strong community, extensive plugin system and huge flexibility, we advocate for using it on most our projects.
Front-end libraries and frameworks
Depending on the project needs, we typically use either React or Angular. Both are great options, and our choice usually comes down to the needs of the project.
Even though React is just a view layer for your app, it has a great ecosystem many add-ons for the the model/controller layer to build more complex apps, such as Redux or MobX.
By contrast, Angular comes with a lot of pre-defined structure and tells you how to lay out your app and components. It also enables developers to write more HTML-like code with React, and is a great choice when prototyping app ideas quickly.