This inheritance list is sorted roughly, but not completely, alphabetically:
CI_Benchmark
CI_Calendar
CI_Config
CI_DB_Cache
CI_DB_driver
CI_DB_active_record
CI_DB_forge
CI_DB_mssql_forge
CI_DB_mysql_forge
CI_DB_mysqli_forge
CI_DB_oci8_forge
CI_DB_odbc_forge
CI_DB_postgre_forge
CI_DB_sqlite_forge
CI_DB_utility
CI_DB_mssql_utility
CI_DB_mysql_utility
CI_DB_mysqli_utility
CI_DB_oci8_utility
CI_DB_odbc_utility
CI_DB_postgre_utility
CI_DB_sqlite_utility
CI_DB_mssql_driver
CI_DB_mysql_driver
CI_DB_mysqli_driver
CI_DB_oci8_driver
CI_DB_odbc_driver
CI_DB_postgre_driver
CI_DB_result
CI_DB_mssql_result
CI_DB_mysql_result
CI_DB_mysqli_result
CI_DB_oci8_result
CI_DB_odbc_result
CI_DB_postgre_result
CI_DB_sqlite_result
CI_DB_sqlite_driver
CI_Email
CI_Encrypt
CI_Exceptions
CI_Form_validation
CI_FTP
CI_Hooks
CI_Image_lib
CI_Input
CI_Language
CI_Loader
CI_Base
Controller
Welcome
CI_Log
CI_Output
CI_Pagination
CI_Parser
CI_Profiler
CI_Router
CI_Session
CI_SHA
CI_Table
CI_Trackback
CI_Typography
CI_Unit_test
CI_Upload
CI_URI
CI_User_agent
CI_Validation
CI_Xmlrpc
CI_Xmlrpcs
XML_RPC_Client
XML_RPC_Message
XML_RPC_Values
CI_Zip
Model
Scaffolding
XML_RPC_Response
