Windows SharePoint Services (WSS) is a free add-on to Windows Server 2003 made available by Microsoft. It offers basic web portal and intranet functionality, including portal pages called web part pages made up of web parts (developed in ASP.NET), team, document or project sub-sites, version-controlled document storage, and basic search functionality. It is made up of an ASP.NET web site hosted on Internet Information Services 6.0, using a Microsoft SQL Server or Microsoft SQL Server Desktop Engine (MSDE) database back-end to store data. Windows SharePoint Services also forms the basis for Microsoft Office SharePoint Portal Server and Microsoft Office Project Server. Portal Server is the enterprise layer (not free) that is built upon Windows SharePoint Services.