The .NET (note capitalization) initiative is a Microsoft project to create a new software development platform focused on network transparency, platform independence, and rapid application development.
.NET is Microsoft's strategic initiative for server and desktop development for the next decade. According to Microsoft, .NET includes many technologies that are designed to facilitate rapid development of Internet applications.
Second, .NET is a software platform, which was released in 2002. It presents a platform-independent target for software development, with many built-in features including Internet integration and features intended to enhance security. It relies fully on software componentry and the component-oriented programming paradigm. In this respect it largely replaces the former component object model (COM).
Third, .NET is a collection of development tools specifically developed for use with the .NET platform. The principal example being Visual Studio, an integrated development environment provided by Microsoft.
The CLI is designed to provide support for any object-oriented programming language, sharing a common object model and a large common class library.
Microsoft and other vendors provide .NET versions of many languages, including:
Notes:
The Microsoft support resource MSDN is emphasizing the .NET languages.
The CLI, the CIL and C# have similarities to Sun Microsystems' Java Virtual Machine and Sun's Java, hence they are fierce competitors. Both use their own intermediate bytecode. .NET bytecode is designed for JITing, while Java bytecode originally was designed to be interpreted not JITTED. .NET is currently only fully available on Windows platforms, whereas Java is available on many platforms. (However, see below for alternative implementations such as Mono or Rotor.) Sun's product, J2EE, provides equivalent functionality to other Microsoft technologies such as COM+ (previously MTS) and MSMQ which are tightly integrated into the Windows operating system. .NET components make full use of these existing technologies in an abstracted manner.
The previous software component technology endorsed by Microsoft for large-scale software systems was the Component object model or COM, using COM+ or MTS enhancements for distributed transactional components. While .NET may wrap COM-objects and vice versa, it has been clearly stated by Microsoft that .NET will eventually replace COM as a software component architecture. New applications addressing the Win32 platform should not use COM, but .NET, with use of existing services via abstracted interfaces (e.g. transactional .Net components currently use COM+).
Microsoft has submitted a part of the specifications of .NET to ECMA and ISO for standardization. This is a calculated risk, but it may encourage standards-compliant implementations, to provide an ongoing bridge for non-Windows software to be converted to Microsoft .NET.
While the Microsoft .NET Framework is the flagship implementation of .NET technologies, there exist other implementations.
Mono is an open source implementation of the .NET runtime and development libraries. It is quickly maturing, including support for ASP.NET and evolving support for Windows Forms libraries. Mono also includes the development of new libraries and technologies, which include:
DotGNU Portable.NET is less mature than Mono due to the fact that Portable.NET was not written initially using Microsoft's development framework.
Microsoft Rotor, or the Shared Source Common Language Infrastructure is a shared source implementation of the .NET Framework by Microsoft. It runs on Microsoft Windows XP, FreeBSD, and Mac OS X 10.2.