SQL Server Compact 3.5
SQL Server Compact 3.5 is a compact yet powerful embedded database for enabling users with a new generation of occasionally connected dynamic applications. Free, lightweight and embeddable, SQL Server Compact 3.5 offers essential relational database functionality to build a new generation of occasionally connected mobile and desktop applications.
(Note: SQL Server 2005 Compact Edition is the earlier version of SQL Server Compact 3.5 and was previously named SQL Server 2005 Everywhere Edition during the product development phase. You may see references to the name SQL Server 2005 Everywhere Edition in pre-recorded material for SQL Server 2005 Compact Edition.)
SQL Server Compact Software
Developer Tools and SDK