Ember with Node (MEEN stack?)
If you're coming from Rails I'd break it down like this:
node.js -> Ruby - your server side language / platform
express -> Rails - your server side framework, although a little more like Sinatra
grunt -> Rake - your preprocessor / build tool
npm -> gem - your server side package manager
Angular.js / Ember.js -> No direct map, your client side framework.
mongoose.js -> ActiveRecord, but for MongoDb. If you want a SQL ORM use Sequelize
Two other tools worth learning are
bower -> your client side package manager, for things like bootstrap
yeoman -> all round js app scaffolding, ties everything together, a great tool to see how to scaffold "best practice" apps.