I have moved this list to the postgresql [http://www.postgresql.org/docs/techdocs.62 techdocs], although I reduced to not cover postgres anymore.

||~ Name ||~ License ||~ Notes ||
|| Illustra || proprietary || Fork of Postgres ||
|| [http://www.postgresql.org/ PostgreSQL] || BSD || Open source community project ||
|| [http://sources.redhat.com/rhdb/ Red Hat Database] || BSD || PostgreSQL re-distribution ||
|| [http://www.pervasive-postgres.com/ Pervasive PostgreSQL] || BSD || PostgreSQL re-distribution ||
|| [http://greenplum.com/products/bizgresMpp.php BizgresMPP] || proprietary || PostgreSQL + BI features ||
|| [http://www.bizgres.org Bizgres] || BSD || PostgreSQL + BI features ||
|| [http://www.mammothpostgresql.org/ Mammoth] || BSD || PostgreSQL + contrib modules ||
|| [http://www.netezza.com/ Netezza] || proprietary || Appliance based on PG’s SQL engine ||
|| [http://www.paraccel.com/ parACCEL] || proprietary || PostgreSQL + BI features ||
|| [http://telegraph.cs.berkeley.edu/ TelegraphCQ] || BSD || Data Stream oriented fork of PostgresSQL ||
|| [http://www.sraapowergres.com PowerGres] || proprietary || Native Win32 port of PostgreSQL ||
|| [http://software.fujitsu.com/jp/powergresplus PowerGres Plus] || proprietary || PostgreSQL + custom storage engine ||
|| [http://www.sun.com/software/solaris/postgresql.jsp PostgreSQL for Solaris 10] || BSD || PostgreSQL re-distribution ||
|| [http://www.greatbridge.com/ Great Bridge PostgreSQL] || BSD || PostgreSQL re-distribution ||
|| [http://enterprisedb.com/ EnterpriseDB] || proprietary || PostgreSQL + Oracle compatibility ||
|| [http://www.aminsight.com/ Amalgamated Insight] || proprietary || Fork of TelegraphCQ ||
|| [http://www.nusphere.com/products/ultrasql.htm NuSphere UltraSQL] || proprietary || Native Win32 port of PostgreSQL ||