As described on the Code Synthesis product page, "ODB is an open-source, cross-platform, and cross-database object-relational mapping (ORM) system for C++. It allows you to persist C++ objects to a relational database without having to deal with tables, columns, or SQL and without manually writing any mapping code...ODB is not a framework. It does not dictate how you should write your application. Rather, it is designed to fit into your style and architecture by only handling C++ object persistence and not interfering with any other functionality."
ODB is designed to be very easy to use, produce concise code, utilizes static typing and other maneuvers for safety, portable between database systems, designed for optimal performance, and allow for sufficient code maintainability.
Code Synthesis implements ODB as a GCC plug-in and re-uses the GCC compiler front-end for C++ parsing. For open-source database systems, Code Synthesis makes the ODB C++ ORM available for free and under the terms of the GPLv2.
New to the 2.2 release that was made available today includes support for multiple database systems within the same application, suppoer for prepared queries, support for change-tracking containers, support for custom sessions, support for automatically-derived SQL name transformations, and automatic mapping for database field sizes. Version 2.2 also adds in support for Qt5.
Aside from the aforelinked product page, more information on ODB C++ ORM 2.2 can be found from this mailing list announcement.