The internal code name for the .NET Framework was NGWS, short for Next Generation Windows Services.
Microsoft began developing the platform in the late 1990s as part of its broader .NET strategy. During this early period, the project was known as Next Generation Windows Services, abbreviated NGWS. The name described Microsoft's goal of creating a modern Windows software platform built around managed code and reusable services.
The project evolved into the .NET Framework, whose first release arrived in 2002. It provided the Common Language Runtime, a large Framework Class Library, and language interoperability, allowing languages such as C#, Visual Basic .NET, and others to use common runtime services and libraries.
The other options were names associated with different Microsoft technologies. Avalon was the codename for Windows Presentation Foundation, Indigo was associated with Windows Communication Foundation, and WinFS was a proposed data-storage subsystem. They were not the original internal name of the .NET Framework.
.NET Framework should also be distinguished from the newer, cross-platform .NET platform, which Microsoft developed after the Framework became primarily associated with Windows.