CodeIgniter ver.3で準備されているClass群を調べてみた。
※ CI_Cart、CI_Javascript、CI_Jqueryはdeprecated.(CI_JqueryはCI_Javascriptを継承している。)

CodeIgniter
Upgrading From a Previous Version
the-cart-library
the-javascript-library

class extends file
CI_Benchmark system\core\Benchmark.php
CI_Config system\core\Config.php
CI_Controller system\core\Controller.php
CI_Exceptions system\core\Exceptions.php
CI_Hooks system\core\Hooks.php
CI_Input system\core\Input.php
CI_Lang system\core\Lang.php
CI_Loader system\core\Loader.php
CI_Log system\core\Log.php
CI_Model system\core\Model.php
CI_Output system\core\Output.php
CI_Router system\core\Router.php
CI_Security system\core\Security.php
CI_URI system\core\URI.php
CI_Utf8 system\core\Utf8.php
CI_DB_Cache system\database\DB_cache.php
CI_DB_result system\database\DB_result.php
CI_DB_cubrid_driver extends CI_DB system\database\drivers\cubrid\cubrid_driver.php
CI_DB_cubrid_forge extends CI_DB_forge system\database\drivers\cubrid\cubrid_forge.php
CI_DB_cubrid_result extends CI_DB_result system\database\drivers\cubrid\cubrid_result.php
CI_DB_cubrid_utility extends CI_DB_utility system\database\drivers\cubrid\cubrid_utility.php
CI_DB_ibase_driver extends CI_DB system\database\drivers\ibase\ibase_driver.php
CI_DB_ibase_forge extends CI_DB_forge system\database\drivers\ibase\ibase_forge.php
CI_DB_ibase_result extends CI_DB_result system\database\drivers\ibase\ibase_result.php
CI_DB_ibase_utility extends CI_DB_utility system\database\drivers\ibase\ibase_utility.php
CI_DB_mssql_driver extends CI_DB system\database\drivers\mssql\mssql_driver.php
CI_DB_mssql_forge extends CI_DB_forge system\database\drivers\mssql\mssql_forge.php
CI_DB_mssql_result extends CI_DB_result system\database\drivers\mssql\mssql_result.php
CI_DB_mssql_utility extends CI_DB_utility system\database\drivers\mssql\mssql_utility.php
CI_DB_mysql_driver extends CI_DB system\database\drivers\mysql\mysql_driver.php
CI_DB_mysql_forge extends CI_DB_forge system\database\drivers\mysql\mysql_forge.php
CI_DB_mysql_result extends CI_DB_result system\database\drivers\mysql\mysql_result.php
CI_DB_mysql_utility extends CI_DB_utility system\database\drivers\mysql\mysql_utility.php
CI_DB_mysqli_driver extends CI_DB system\database\drivers\mysqli\mysqli_driver.php
CI_DB_mysqli_forge extends CI_DB_forge system\database\drivers\mysqli\mysqli_forge.php
CI_DB_mysqli_result extends CI_DB_result system\database\drivers\mysqli\mysqli_result.php
CI_DB_mysqli_utility extends CI_DB_utility system\database\drivers\mysqli\mysqli_utility.php
CI_DB_oci8_driver extends CI_DB system\database\drivers\oci8\oci8_driver.php
CI_DB_oci8_forge extends CI_DB_forge system\database\drivers\oci8\oci8_forge.php
CI_DB_oci8_result extends CI_DB_result system\database\drivers\oci8\oci8_result.php
CI_DB_oci8_utility extends CI_DB_utility system\database\drivers\oci8\oci8_utility.php
CI_DB_odbc_driver extends CI_DB system\database\drivers\odbc\odbc_driver.php
CI_DB_odbc_forge extends CI_DB_forge system\database\drivers\odbc\odbc_forge.php
CI_DB_odbc_result extends CI_DB_result system\database\drivers\odbc\odbc_result.php
CI_DB_odbc_utility extends CI_DB_utility system\database\drivers\odbc\odbc_utility.php
CI_DB_pdo_driver extends CI_DB system\database\drivers\pdo\pdo_driver.php
CI_DB_pdo_forge extends CI_DB_forge system\database\drivers\pdo\pdo_forge.php
CI_DB_pdo_result extends CI_DB_result system\database\drivers\pdo\pdo_result.php
CI_DB_pdo_utility extends CI_DB_utility system\database\drivers\pdo\pdo_utility.php
CI_DB_pdo_4d_driver extends CI_DB_pdo_driver system\database\drivers\pdo\subdrivers\pdo_4d_driver.php
CI_DB_pdo_4d_forge extends CI_DB_pdo_forge system\database\drivers\pdo\subdrivers\pdo_4d_forge.php
CI_DB_pdo_cubrid_driver extends CI_DB_pdo_driver system\database\drivers\pdo\subdrivers\pdo_cubrid_driver.php
CI_DB_pdo_cubrid_forge extends CI_DB_pdo_forge system\database\drivers\pdo\subdrivers\pdo_cubrid_forge.php
CI_DB_pdo_dblib_driver extends CI_DB_pdo_driver system\database\drivers\pdo\subdrivers\pdo_dblib_driver.php
CI_DB_pdo_dblib_forge extends CI_DB_pdo_forge system\database\drivers\pdo\subdrivers\pdo_dblib_forge.php
CI_DB_pdo_firebird_driver extends CI_DB_pdo_driver system\database\drivers\pdo\subdrivers\pdo_firebird_driver.php
CI_DB_pdo_firebird_forge extends CI_DB_pdo_forge system\database\drivers\pdo\subdrivers\pdo_firebird_forge.php
CI_DB_pdo_ibm_driver extends CI_DB_pdo_driver system\database\drivers\pdo\subdrivers\pdo_ibm_driver.php
CI_DB_pdo_ibm_forge extends CI_DB_pdo_forge system\database\drivers\pdo\subdrivers\pdo_ibm_forge.php
CI_DB_pdo_informix_driver extends CI_DB_pdo_driver system\database\drivers\pdo\subdrivers\pdo_informix_driver.php
CI_DB_pdo_informix_forge extends CI_DB_pdo_forge system\database\drivers\pdo\subdrivers\pdo_informix_forge.php
CI_DB_pdo_mysql_driver extends CI_DB_pdo_driver system\database\drivers\pdo\subdrivers\pdo_mysql_driver.php
CI_DB_pdo_mysql_forge extends CI_DB_pdo_forge system\database\drivers\pdo\subdrivers\pdo_mysql_forge.php
CI_DB_pdo_oci_driver extends CI_DB_pdo_driver system\database\drivers\pdo\subdrivers\pdo_oci_driver.php
CI_DB_pdo_oci_forge extends CI_DB_pdo_forge system\database\drivers\pdo\subdrivers\pdo_oci_forge.php
CI_DB_pdo_odbc_driver extends CI_DB_pdo_driver system\database\drivers\pdo\subdrivers\pdo_odbc_driver.php
CI_DB_pdo_odbc_forge extends CI_DB_pdo_forge system\database\drivers\pdo\subdrivers\pdo_odbc_forge.php
CI_DB_pdo_pgsql_driver extends CI_DB_pdo_driver system\database\drivers\pdo\subdrivers\pdo_pgsql_driver.php
CI_DB_pdo_pgsql_forge extends CI_DB_pdo_forge system\database\drivers\pdo\subdrivers\pdo_pgsql_forge.php
CI_DB_pdo_sqlite_driver extends CI_DB_pdo_driver system\database\drivers\pdo\subdrivers\pdo_sqlite_driver.php
CI_DB_pdo_sqlite_forge extends CI_DB_pdo_forge system\database\drivers\pdo\subdrivers\pdo_sqlite_forge.php
CI_DB_pdo_sqlsrv_driver extends CI_DB_pdo_driver system\database\drivers\pdo\subdrivers\pdo_sqlsrv_driver.php
CI_DB_pdo_sqlsrv_forge extends CI_DB_pdo_forge system\database\drivers\pdo\subdrivers\pdo_sqlsrv_forge.php
CI_DB_postgre_driver extends CI_DB system\database\drivers\postgre\postgre_driver.php
CI_DB_postgre_forge extends CI_DB_forge system\database\drivers\postgre\postgre_forge.php
CI_DB_postgre_result extends CI_DB_result system\database\drivers\postgre\postgre_result.php
CI_DB_postgre_utility extends CI_DB_utility system\database\drivers\postgre\postgre_utility.php
CI_DB_sqlite_driver extends CI_DB system\database\drivers\sqlite\sqlite_driver.php
CI_DB_sqlite_forge extends CI_DB_forge system\database\drivers\sqlite\sqlite_forge.php
CI_DB_sqlite_result extends CI_DB_result system\database\drivers\sqlite\sqlite_result.php
CI_DB_sqlite_utility extends CI_DB_utility system\database\drivers\sqlite\sqlite_utility.php
CI_DB_sqlite3_driver extends CI_DB system\database\drivers\sqlite3\sqlite3_driver.php
CI_DB_sqlite3_forge extends CI_DB_forge system\database\drivers\sqlite3\sqlite3_forge.php
CI_DB_sqlite3_result extends CI_DB_result system\database\drivers\sqlite3\sqlite3_result.php
CI_DB_sqlite3_utility extends CI_DB_utility system\database\drivers\sqlite3\sqlite3_utility.php
CI_DB_sqlsrv_driver extends CI_DB system\database\drivers\sqlsrv\sqlsrv_driver.php
CI_DB_sqlsrv_forge extends CI_DB_forge system\database\drivers\sqlsrv\sqlsrv_forge.php
CI_DB_sqlsrv_result extends CI_DB_result system\database\drivers\sqlsrv\sqlsrv_result.php
CI_DB_sqlsrv_utility extends CI_DB_utility system\database\drivers\sqlsrv\sqlsrv_utility.php
CI_Calendar system\libraries\Calendar.php
CI_Cart system\libraries\Cart.php
CI_Driver_Library system\libraries\Driver.php
CI_Driver system\libraries\Driver.php
CI_Email system\libraries\Email.php
CI_Encrypt system\libraries\Encrypt.php
CI_Encryption system\libraries\Encryption.php
CI_Form_validation system\libraries\Form_validation.php
CI_FTP system\libraries\Ftp.php
CI_Image_lib system\libraries\Image_lib.php
CI_Javascript system\libraries\Javascript.php
CI_Migration system\libraries\Migration.php
CI_Pagination system\libraries\Pagination.php
CI_Parser system\libraries\Parser.php
CI_Profiler system\libraries\Profiler.php
CI_Table system\libraries\Table.php
CI_Trackback system\libraries\Trackback.php
CI_Typography system\libraries\Typography.php
CI_Unit_test system\libraries\Unit_test.php
CI_Upload system\libraries\Upload.php
CI_User_agent system\libraries\User_agent.php
CI_Xmlrpc system\libraries\Xmlrpc.php
XML_RPC_Client extends CI_Xmlrpc system\libraries\Xmlrpc.php
XML_RPC_Response system\libraries\Xmlrpc.php
XML_RPC_Message extends CI_Xmlrpc system\libraries\Xmlrpc.php
XML_RPC_Values extends CI_Xmlrpc system\libraries\Xmlrpc.php
CI_Xmlrpcs extends CI_Xmlrpc system\libraries\Xmlrpcs.php
CI_Zip system\libraries\Zip.php
CI_Cache extends CI_Driver_Library system\libraries\Cache\Cache.php
CI_Cache_apc extends CI_Driver system\libraries\Cache\drivers\Cache_apc.php
CI_Cache_dummy extends CI_Driver system\libraries\Cache\drivers\Cache_dummy.php
CI_Cache_file extends CI_Driver system\libraries\Cache\drivers\Cache_file.php
CI_Cache_memcached extends CI_Driver system\libraries\Cache\drivers\Cache_memcached.php
CI_Cache_redis extends CI_Driver system\libraries\Cache\drivers\Cache_redis.php
CI_Cache_wincache extends CI_Driver system\libraries\Cache\drivers\Cache_wincache.php
CI_Jquery extends CI_Javascript system\libraries\Javascript\Jquery.php
CI_Session system\libraries\Session\Session.php
CI_Session_database_driver extends CI_Session_driver implements SessionHandlerInterface system\libraries\Session\drivers\Session_database_driver.php
CI_Session_files_driver extends CI_Session_driver implements SessionHandlerInterface system\libraries\Session\drivers\Session_files_driver.php
CI_Session_memcached_driver extends CI_Session_driver implements SessionHandlerInterface system\libraries\Session\drivers\Session_memcached_driver.php
CI_Session_redis_driver extends CI_Session_driver implements SessionHandlerInterface system\libraries\Session\drivers\Session_redis_driver.php

とりあえず、ここまで。