Can you explain what Flutter is and how it is used for app development?

Flutter is a framework from Google for developing cross-platform mobile, web, and desktop applications with a single codebase in the Dart language.

Main features of Flutter:

• Uses its own rendering engine, allowing the creation of high-performance and beautiful interfaces.
• Enables declarative UI development with widgets.
• Provides "hot reload" for rapid development.

Example of using Flutter to create a simple application:

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(title: Text('Flutter Example')),
        body: Center(child: Text('Hello, Flutter!')),
      ),
    );
  }
}

Thus, Flutter is used for fast and convenient development of applications with a single codebase for different platforms.