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:
http://mono-project.com/Cecil Mono.Cecil (MIT/X11)
Used inside Db4objects.Db4o.Tools.dll
Cecil is used to read the CIL code during native queries optimization.
http://mono-project.com/Cecil Cecil.FlowAnalysis (MIT/X11)
Used inside Db4objects.Db4o.Tools.dll
Cecil.FlowAnalysis is used to analyse the CIL code during native queries optimization.
http://mono-project.com/ Mono.GetOptions (MIT/X11)
Used inside Db4oAdmin.exe
Mono.GetOptions is used to parse the command line of the Db4oAdmin.exe tool.