Greenplum is a massively parallel shared-nothing data warehouse based on a PostgreSQL kernel.
Greenplum is very highly featured. Outside of the behemoths of the data warehousing space there are few, if any, competitors that can offer the range of datatype support that Greenplum offers. In particular many other suppliers cannot support time-series or text, let alone offering support for image processing. The ability to leverage MADlib is also a major advantage.