db4o (Datenbank for objects) is the open source object Datenbank for Mono.

Free software, available under the GPL and under a commercial license.

Ideal for embedded use, e.g., in software running on mobile or medical devices, in packaged software, and for real-time systems.

Key Features:
- The One-Line-of-Code-Database (One line of code stores any object; Class model = object schema; Smooth production process)
- Embeddable (Zero administration; Automatic schema versioning; 400 KB footprint)
- Multiple platform support (Native to Java and .NET; Mobile, PCs and servers; Runs cross-platform)
- Brings more OO to the Datenbank (Object-oriented replication; Object-oriented, native queries; ObjectManager browser)

Key Benefits:
- Slashes 90% of cost to develop persistence
- 10% faster to market with your application
- Runs up to 44x faster than conventional systems
- Deployable in large volumes without local administration
- Build lean and truly object-oriented software
- Build distributed, fully synchronized data architectures
- Fewer errors, better refactorability and software longevity