SQL Server Express is a free, easy to use, redistributable version of SQL Server 2005 designed for building simple data-driven applications. Developers can design schemas, add data, and query local databases, and perform most of the features supported by SQL Server 2005. If developers need more advanced database features, then SQL Server Express can be seamlessly upgraded to more sophisticated versions of SQL Server.
Microsoft SQL Server 2005 Express Edition (SQL Server Express) is a database platform that is based on Microsoft SQL Server 2005. It is also a replacement for Microsoft Desktop Engine (MSDE).
SQL Server Express comes with a graphical user interface to manage the database system. It is called 'SQL Server Management Studio Express".
SQL Server Express and Management Studio Express are free to download and distribute. If you like to upgrade SQL Server Express databases to full version of SQL Server, it is very straight forward. Just install SQL Server 2005 and your databases and code will work without any changes.
You can download SQL Server Express and Management Studio Express from Microsoft website.
If you are looking for a free, powerful database system for your application, SQL Server Express if the way to go!