SQL Server 2014 Developer Edition is free - but you'll need to register. https://my.visualstudio.com/Downloads?q=SQL%20Server%202014%20Developer
See announcement for more details and links: https://blogs.technet.microsoft.com/dataplatforminsider/2016/03/31/microsoft-sql-server-developer-edition-is-now-free/
Thomas Rushton
blog: https://thelonedba.wordpress.com