SQL Server Code Name "Denali" Express CTP3 is a free edition of SQL Server that is ideal for learning, developing and powering desktop, web and small server applications, and for redistribution by ISVs.
New in this release is SQL Server Express LocalDB. LocalDB is a lightweight version of Express that has all of its programmability features, yet runs in user mode and has a fast, zero-configuration installation and a short list of pre-requisites. To try LocalDB, simply check the box during the installation process of either SQL Server Express option.
Check the link below to download the setup
SQL Server Code Name Denali Express CTP3