Node.js

Why then? Node is made possible by Google's open-source V8 open-source Javascript engine. Both come out in 2008. It also benefits from ES5 being finalized in 2009.

V8 uses just-in-time compiling to translate Javascript code into native machine operations. Having a compilation step gives a place to hook in a lot of tooling that makes development easier.

And Javascript running in V8 is fast. Node is initially proposed as an alternative to the Apache web server, which is written in C.