Here are some Node.js apps that are famous for their scale and ridiculous performance.
Walmart switched over to Node.js on a Black Friday, got more than 200 million visitors that day, and never went above 1% CPU.
LinkedIn rewrote their mobile backend in Node.js, and proceeded to get 20 times the performance out of 1/10 the servers.
Groupon increased page load speed by 50% by switching from Ruby on Rails to Node.js. They also reported being able to launch new features much faster than before.
Paypal did an experiment where two teams built identical apps – one in Java and one in Node.js. The Node.js team built theirs in half the time. The Node.js app had response times that were 50% faster than the Java app.
You can read more about these incredible performance gains (and developer productivity gains)
IBM X-Force Exchange:
The backend (API) runs on Node.js in a CloudFoundry environment. This makes it easy to scale the whole thing horizontally and vertically on demand. The backend handles over 700 TB of Threat Intelligence data for thousands of customers: in a single(!) thread. [IBM X-Force Exchange]
Amazon uses node.js for certain services in their backend. Their newest website is also based on Angular.js. It is likely that their frontend is served by a simple node.js webserver instance. [At least you can use node in AWS: Node.js]
Many companies and projects are switching to Node.js like: