Last year, Microsoft announced Visual Studio Dev Essentials which provides free versions of Visual Studio and other Microsoft development tools to registered users. Recently, the Developer Edition of SQL Server 2014 was added as a free download to this program (and SQL Server 2016 Developer Edition will be free as well when available). If you are signed up for Dev Essentials, you can now download and use Developer Edition for free for your personal training or development work.
Read the official announcement for the SQL Server Team: https://blogs.technet.microsoft.com/dataplatforminsider/2016/03/31/microsoft-sql-server-developer-ed...
Sign up for Dev Essentials today: https://www.visualstudio.com/products/visual-studio-dev-essentials-vs
Please note that Developer Edition is not allowed to be used for production or commercial purposes.