DAX Studio (Free)
Excel Add-In for PowerPivot and Analysis Services Tabular projects that will include an Object Browser, query editing and execution, formula and measure editing ,syntax highlighting, integrated tracing and query execution breakdowns.
DAX Studio is not a Microsoft Product and is not supported by Microsoft Personnel. It is developed and maintained only by people on this project site only. If you have any feedback, recommendations or issues with DAX Studio, please add them to this project site.
Read: Introducing DAX Studio by Paul te Braak
Read: Using DAX Studio to create PowerPivot measures by Javier Guillen
Read: DAX Studio review by MS SQL Girl