The Greenplum database by EMC, is based on PostgreSQL, and has done a good job at keeping compatibility with PostgreSQL on the protocol layer and the system catalog level. For this reason, Greenplum bundles pgAdmin as the GUI client and also includes the PostgreSQL JDBC driver. To a PostgreSQL GUI there is no difference between PostgreSQL and Greenplum. This has provided Greenplum an instant set of PostgreSQL Open Source tools for compatibility. Many Aqua Data Studio users used the PostgreSQL interface for connecting to Greenplum. This compatibility made it easier for us to add extended support for Greenplum. With the new Greenplum connection in Aqua Data Studio we use the PosgreSQL JDBC Driver to make a JDBC connection and then use Greenplum specific DDL and System Catalog tables. The DDL and System Catalog tables of Greenplum do have extensions to the PostgreSQL base for support of its distributed nature. Aqua Data Studio 13.0 is the first fully supporting GUI to the Greenplum database.
From our web research it has been hard to determine who originally designed Greenplum. We did find a good blog post by one of the early investors in Greenplum which you can read in the link below. According to the Greenplum website, the co-founders of Greenplum were Scott Yara and Luke Lonergan. Luke Lonergan started a database clustering company called Didera which was acquired by Metapa, which later renamed itself Greenplum. From the blog post it would seem that Greenplum went through a few re-implementations. It is hard to get things right the first time.
The PostgreSQL project was started in the 80's, while Greenplum was built off of PostgreSQL in the early 2000's, so you can see Greenplum as PostgreSQL's little brother. But the little stops there as Greenplum is specifically built for Big Data to scale across a cluster of machines. Using a combination of PostgreSQL and Greenplum in your enterprise can provide a good combination of both transactional and analytical capabilities. The compatibility between the two platforms enables you to standardize your tools and applications and helps in lowering the costs of trainings and migrations. EMC even offers a free community edition of Greenplum to get you started on development and training. PostgreSQL was designed and released as an Open Source product. This has spawned commercial product innovations with Greenplum, nCluster, ParAccel and others. Hopefully some of the commercial innovations will make it into PostgreSQL one day.