Crescent is the code name the new business intelligence user interface Microsoft intends to release with the Denali release of SQL Server. You may have heard about it, because Microsoft has been releasing excited videos about it, featuring huge crowds of developers going wild over the technology. I have not seen much of the technology itself, but what I have seen seems to borrow heavily on the user interfaces of Tableau and the Google Data Explorer.
The technology is closely related to PowerPivot. It is based on a new hybrid semantic layer that either directly access a data source or uses PowerPivot's Vertipaq column-oriented storage engine. It is part of Microsoft's not yet fully realized plan to provide seamless conversion of Excel-based data marts to a server environment.
To me, the most intriguing thing about SQL Crescent is that Microsoft's SQL development team is dipping its toe into the area of business intelligence front ends. (I don't really include Reporting Services because it is simply a reporting tool, not a specialized BI tool, and it works better with relational data than with multidimensional data.) In the past real analysis has been the domain of the Office group. PerformancePoint was a bit of a halfway house between the groups, but in the end it was folded into SharePoint, where the dashboard component still resides. Currently PowerPivot only has an Excel (or SharePoint Excel Services) user interface. So this seems like a big step.