An object database management system (ODBMS, also referred to as object-oriented database management system or OODBMS), is a database management system (DBMS) that supports the modelling and creation of data as objects. This includes some kind of support for classes of objects and the inheritance of class properties and methods by subclasses and their objects.
db4o is an object database, native to Java and for .NET, including CompactFramework and Mono.
Features include ACID transactions, automatic class schema recognition, Native Queries, small footprint, and many more, that make it ideal for embedded use in devices, packaged software and realtime systems.