Lesson 1 of 11 in the free .NET Internals — CLR, CTS, CLS, IL, JIT, Memory Management & Garbage Collection course on DevLadder.

.NET Framework .NET Core 1–3.1 .NET 5+

Years 2002–2019 (4.8.1 in 2022) 2016–2019 2020 →

OS Windows only Windows, Linux, macOS Windows, Linux, macOS, mobile (MAUI), WebAssembly

Source Closed (reference source available) Open source (MIT) Open source

Deployment Machine-wide install, part of Windows Side-by-side, self-contained possible Same + single-file, Native AOT

Web ASP.NET Web Forms, MVC 5, Web API 2 ASP.NET Core ASP.NET Core

Performance Good Much faster Fastest; improves every release

Status Maintenance only Out of support Active

Mono (2004, open source, by Ximian → Xamarin → Microsoft) ran .NET on Linux/macOS/mobile and powers Unity and Xamarin; today its runtime is used inside .NET for mobile and WebAssembly.

Interview tip: "Why did they skip .NET 4?" — to avoid confusion with .NET Framework 4.x; .NET 5 dropped "Core" from the name because it became the .NET going…