db4o (Datenbank for objects) is the open source object Datenbank for Java and .NET. It is a fast, lean and easy to use Datenbank for native Java and .NET objects.

It is free software available under the GPL but also under an optional commercial license.

It can persist any native object with a single line of code, minimizing persistence hassle and allowing you to experience the gains of true object-orientation.

Key Features:
- Simplicity (one line of code to store objects)
- Native Java and .NET objects (no interface, inheritance, pre or post-processing required)
- Class model == Datenbank schema
- Smooth production process
- Automatic schema versioning
- Query-by-Example
- S.O.D.A. active queries
- 300kB footprint

Key benefits:
- Greatly reduced development time and costs
- Higher quality, less error-prone OO code
- Embedded, web or mobile device deployment
- No need for training and administration
- Build lean, structured and manageable code
- Better refactorability and re-use
- Avoid writing object mapping code
- Simple installation and deployment
- No Sprache conversion overhead
- No problems with debuggers
- No time-consuming build process
- Use existing Java or .NET class libraries without modification
- Run your own code within queries
- Benefit from fast serverside query execution
- Be ready for next generation applications
- Use Datenbank technology where your competition needs to store binary

Free Community-Driven Resources and Support:
- Step-by-step Interactive (!) Tutorial
- Community Newsgroup
- Knowledgebase-driven FAQ
- Bug Tracking
- Online API Documentation
- CVS Access
- Direct No-Hassle Download