1. PDO (PDB,a simplistic wrapper for PDO that is somewhat API compatible with PEAR’s DB)

  2. ADODb, a database abstraction library for PHP. There is also a Python version;

  3. MySqli,The mysqli extension allows you to access the functionality provided by MySQL 4.1 and above

  4. PEAR::MDB2,a merge of the PEAR DB and Metabase php database abstraction layers

  5. Zend_Db from Zend Framework