Greenplum SNE (Single Node Edition) is a free version of the Greenplum database.
It is based on PostgreSQL 8.2.11. technology and a solution for data warehousing and analytics. It’s using a shared nothing architecture concept and allows for data distribution and parallel processing on several nodes (servers).
The Single Node edition of Greenplum is a freely distributed version of Greenplum which can be installed on a single node. It can be downloaded for free. On a multi-processor architecture, Greenplum Single Node Edition allows to create multiple segments so that one can take advantage of parallel processing. (One segment is one PostgreSQL instance.) You can use the fact that Greenplum is based on PostgreSQL for administering it, i.e the popular (also open source) pgadmin3 GUI Tool (pgadmin3 download) is working pretty well with it. Although it has it flaws, eg. it freezes if you use it with partitioned tables, but it’s great to get just a quick overview.
Also, you can use the PostgreSQL documentation, which applies also for most of Greenplum things as well.

Install instructions