User limit: 1

Redistributable: Yes

Supported platforms: Windows 2000 SP4, Windows Server 2003 SP1, Windows XP SP2

URL: http://msdn.microsoft.com/vstudio/express/sql/ (http://msdn.microsoft.com/vstudio/express/sql/)

While Microsoft's SQL Server continues to make inroads into the enterprise, it's free version, SQL Server 2005 Express Edition has been available for more than a year now. Being a Microsoft product, SQL Server Express is only available for Windows, but support for open standards - including native XML - is a core design feature. In addition to "wizards" for common tasks, SQL Server 2005 Express Edition has a new management and query editing tool. For developers there's "deep integration" with Visual Studio 2005 and Visual Studio data explorer can be used for designing schemas, adding data, and querying local databases. Database specifics aside, SQL Server sure threw down the gauntlet to the incumbent enterprise databases before they all went free.