SQL Server professionals often send me email asking about where can they download the full version of SQL Server for their own development. Microsoft only provides evalution version of its enterprise software (full version). The evaluation version is bound by time and it expires when the time trial is over. This does not work out well when developers want to install the SQL Server into their local machine and try out various features of SQL Server. Additionally, many organizations when they are developing an application do not purchase a full version of the SQL Server. They often prefer to install a free version of the SQL Server and utilize that.
Microsoft does have Express Edition for free but there are many limitations to the product. Additionally, the Express Edition does not have all the features which any enterprise would love to have. Unfortunately Microsoft does not have a full version of SQL Server for developers. However, one can for sure purchase SQL Server Developer Edition for USD 59.95 from Microsoft store. It includes all the functionality of the Enterprise edition, but is licensed for use as a development and test system, not as a production server. SQL Server Developer is an ideal choice for people who build and test applications.
Remember you can’t use this version in your production server but it is a great product to test out various new SQL Server Features.
Reference : Pinal Dave (http://blog.SQLAuthority.com)