MySQL, PostGreSQL, SYBASE, IBM-DB2, Oracle Database and Mongo are widely used databases.
Below are some other databases supported by php
• Cubrid
• DB++
• dBase
• filePro
• FireBird/InterBase
• FrontBase
• Informix
• Ingres
• MaxDB
• mSQL
• Ovrimos SQL
• Paradox
• SQLite
• SQLite3
• SQLSRV
• Tokyo Tyrant