db4o allows using the client/server TCP connection to send
messages from the client to the server. Any object that can be
stored to a db4o database file may be used as a message.
For an example see Reference documentation:
http://developer.db4o.com/Resources/view.aspx/Reference/Client-Server/Messaging
http://developer.db4o.com/Resources/view.aspx/Reference/Client-Server/Remote_Code_Execution