| Horde_History | The Horde_History class provides methods of tracking changes in Horde objects. |
| Horde_History_Composite | A composite implementation of the history storage backend. |
| Horde_History_Exception | Exception handler for the Horde_History library. |
| Horde_History_Log | Class for presenting Horde_History information. |
| Horde_History_Mock | The Horde_History_Mock class provides a method of tracking changes in Horde objects, stored in memory. |
| Horde_History_Mongo | Provides a MongoDB implementation of the history driver. |
| Horde_History_Null | A null implementation of the history storage backend. |
| Horde_History_Sql | The Horde_History_Sql class provides a method of tracking changes in Horde objects, stored in a SQL table. |