Ask HN: Technology Stacks, 2013 edition

These days, there is an absolutely huge number of technologies available to build software. Some of them are proven, others are very much on the bleeding edge to the extent that you can even consider them to be technology showcases.

What are the technologies and underlying system components that are being used in 2013 by startups to build their software ? Let's discuss everything that makes up a full technology stack, from client-side technologies, over programming languages and their libraries to the backend systems.