There are lots of open source
database available. Here is the list of most popular open source database.
1)
MySQL
http://www.mysql.com/
2)
PostgreSQL
http://www.postgresql.org/
3)
Firebird
http://www.firebirdsql.org/
4)
GNU SQL Server
http://panda.ispras.ru/~gsql/
5)
ScimoreDB
http://www.scimore.com/
6)
DXstore database system
http://www.dss.bc.ca/dx/
7)
SAP MaxDB
http://maxdb.sap.com/
8)
HSQLDB
http://hsqldb.org/
9)
CloudDB
http://www.clouddb.org/CloudDB11/
i hope
this are useful for selecting the Open source database.