The .NET Framework is a software platform introduced by Microsoft in 2002 for building and running applications. It originally supported only managed and unmanaged applications focused on Windows Forms and ASP.NET. Over time, the .NET Framework has expanded to include support for additional languages and libraries like JavaScript. The current .NET ecosystem includes .NET Framework, .NET Core, Xamarin, and .NET Standard libraries that can be used across components. Popular languages supported by .NET include C#, VB.NET, C++ and J#.