Your question must be absolutely specific to Windows SharePoint Services 3.0 to have this tag. If uncertain, please include the version in your question text rather than use this tag. Use functionality or feature set in your tags instead of version unless absolutely necessary.
Windows SharePoint Services 3.0 is a free add-on for Windows Server 2003. It comes bundled with Windows Server 2008 where it is now called Microsoft SharePoint Foundation. The non-free enhancement to WSS 3.0 is called MOSS 2007 (Microsoft Office SharePoint Server) which added more features.