.NET Ecosystem and Modern C#

After this lesson, you will be able to: Explain the .NET ecosystem, what you can build with C#, and how modern .NET differs from .NET Framework.

.NET in 2026 is one of the most-used backend platforms in the enterprise. C# is the primary language; .NET 8/9 is cross-platform, open-source, and fast. Unity games + Microsoft shops + finance + healthcare run on it.

This is a free introductory lesson. No purchase required.

What is .NET

.NET (modern, formerly .NET Core, now just '.NET') is a cross-platform runtime + standard library. Runs on Windows, Linux, macOS, ARM. Languages that run on .NET: C# (primary), F# (functional), VB.NET (legacy). C# in 2026 is at version 12, .NET at version 9. Active development since 2002.

.NET vs .NET Framework (the naming mess)

.NET Framework (1.0–4.8): Windows-only, legacy. Last version 2019. Maintenance mode. .NET Core (1.0–3.1) → .NET 5/6/7/8/9: cross-platform, open-source, the present. If a job posting says '.NET Framework 4.7,' it's maintaining legacy. New work is on .NET 8+ (LTS) or .NET 9.

What you can build with C#

Web APIs + backends: ASP.NET Core (very popular for enterprise). Desktop: WPF, WinForms (Windows-only), MAUI (cross-platform). Mobile: MAUI for iOS/Android. Games: Unity (the dominant game engine, C# scripting). Cloud: Azure Functions (first-party Microsoft integration). ML: ML.NET (less common than Python).

Hello, C# (top-level statements, C# 9+)

Save as Program.cs. Run with `dotnet run`.

tsx

// Modern C#: no Main method needed (top-level statements)
Console.WriteLine("Hello, LastWrite!");

var name = "Alex";        // var = type inferred
int age = 30;
bool active = true;

Console.WriteLine($"{name} is {age}");   // string interpolation

// Old-style equivalent:
// using System;
// namespace MyApp {
//     class Program {
//         static void Main(string[] args) {
//             Console.WriteLine("Hello!");
//         }
//     }
// }

Common mistakes only experienced C# devs catch

Confusing .NET Framework with modern .NET. Picking VS Code without the C# Dev Kit (the legacy Omnisharp is unmaintained). Targeting .NET 7 (out of support) instead of .NET 8 LTS in new projects. Old-style 'public static void Main(string[] args)' in C# 10+ files (top-level statements are cleaner).

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