db4objects Inc. supplies the object database engine db4o under a dual licensing regime:
db4o is free to be used:
You should have received a copy of the GPL in the file db4o.license.txt together with the db4o distribution.
If you have questions about when a commercial license is required, please read our GPL Interpretation policy for further detail, available at:
http://www.db4o.com/about/company/legalpolicies/gplinterpretation.aspx
For incorporation into own commercial products and for use together with redistributed software that is not placed under the GPL, db4o is also available under a commercial license.
Visit the purchasing area on the db4o website or contact db4o sales for licensing terms and pricing.
The db4o distribution comes with the following 3rd party libraries:
Apache Ant(Apache Software License)
Files: lib/ant.jar, lib/ant.license.txt
Ant can be used as a make tool for class file based optimization of native queries at compile time.
This product includes software developed by the Apache Software Foundation(http://www.apache.org/).
BLOAT(GNU LGPL)
Files: lib/bloat-1.0.jar, lib/bloat.license.txt
Bloat is used for bytecode analysis during native queries optimization. It needs to be on the classpath during runtime at load time or query execution time for just-in-time optimization. Preoptimized class files are not dependent on BLOAT at runtime.