Windows Server 2003 is the latest step in the evolution of Windows NT from a simple file-and-print server to an application server:

Windows NT 3.1: Microsoft's first 32-bit operating system (OS) and entry into the server space.

Internet Information Services (IIS): Microsoft's Web server; introduced with Internet Server API (ISAPI) for extending the functions of the Web server and evolving to support ASP and ASP.NET for building dynamic Web pages and services.

Microsoft Transaction Server (MTS): introduces server component hosting and transaction monitoring for Windows.

Windows NT 4.0 Option Pack: introduces Microsoft Message Queue (MSMQ) and the merging of IIS, MTS, and other separate application services into Windows OS features.

Windows 2000 Server: introduces COM+ Services, which integrate MTS and MSMQ into a single framework for adding capabilities to server-side COM components.

.NET Framework: introduces new component model, APIs, and the Common Language Runtime.