Node.js 

Node.js is an open-source, cross-platform JavaScript runtime environment that allows for server-side scripting. It is built on Chrome's V8 JavaScript engine.

Key Features

1. Event-Driven Architecture
   - Non-blocking, asynchronous operations.
   - Efficiently handles multiple concurrent connections.

2. Single-Threaded
   - Uses a single-threaded event loop for handling asynchronous tasks.
   - Avoids traditional multi-threading complexities.

3. Non-Blocking I/O
   - Performs I/O operations asynchronously.
   - Ideal for data-intensive real-time applications.

4. npm (Node Package Manager
   - Largest ecosystem of open-source libraries and modules.
   - Facilitates easy sharing and reusing of code.

5. JavaScript for Full-Stack Development
   - Unified language for both client-side and server-side scripting.
   - Simplifies development and reduces context switching.

6. Cross-Platform
   - Compatible with Windows, macOS, and Linux.
   - Offers flexibility in deployment environments.

Common Use Cases

- Web Servers: Create scalable and high-performance web servers.
- APIs and Microservices: Build lightweight and efficient APIs and microservices.
- Real-Time Applications: Develop chat applications, online gaming, collaborative tools, and live streaming services.
- Command-Line Tools: Construct powerful command-line utilities.

Getting Started:

1. Installation:
   - Download from the [official Node.js website](https://nodejs.org/).
   
2. Creating a Simple Server:
javascript
   const http = require('http');
   const server = http.createServer((req, res) => {
     res.statusCode = 200;
     res.setHeader('Content-Type', 'text/plain');
     res.end('Hello World\n');
   });
   server.listen(3000, '127.0.0.1', () => {
     console.log('Server running at http://127.0.0.1:3000/');
   });
   ```

---

This brief note captures the essential aspects of Node.js, including its features, use cases, and a simple example to get started.