The document compares several open source databases: MySQL, PostgreSQL, Firebird, Ingres, MaxDB, and HSQLDB. MySQL is the most widely used but lacks some features. PostgreSQL supports more standards but is slower. Firebird has good Windows support. Ingres and MaxDB are more suitable for large databases or SAP environments respectively. HSQLDB is very fast for simple queries but not large databases. The best choice depends on factors like usage, features, and community support.