Node.js
Node.js is an open-source, cross-platform JavaScript runtime environment that allows developers to execute JavaScript code server-side. It uses the V8 JavaScript engine from Chrome and provides an event-driven, non-blocking I/O model, making it efficient for building scalable network applications. It is commonly used for web servers, APIs, real-time applications, and command-line tools.
Developers should learn Node.js when building backend services, APIs, or real-time applications like chat apps or streaming platforms, as its non-blocking architecture handles high concurrency well. It is also ideal for full-stack JavaScript development, allowing code reuse between frontend and backend, and for microservices due to its lightweight nature and extensive package ecosystem via npm.