Db4objects.Db4o.Optional/dotnet publish -c Release
test/dotnet run

 Build Project will output a jar to ../db4o-gpl/db4o.j/db4o-core/dist/db4o-core.jar
 or Run File, db4o.j/db4o-core/tutorial/src/com/db4odoc/f1/Main.java 

 [user@localhost db4o-core]$ /home/user/netbeans12/extide/ant/bin/ant jar

Db4o-Projects/*/dotnet publish -c Release //like above
Add 4 DLLs in /Output to xamarin-project

var path = Environment.GetFolderPath(Environment.SpecialFolder.Personal);
string dbpath = Path.Combine(path, "x.db");
db = Db4oEmbedded.OpenFile(dbpath);

Project Properities->Android Options->Linking->"Sdk Assemblies Only" (not "Sdk and User Assemblies").
Permission: Read/Write_External_Storage, INTERNET

// <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
// <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
// <uses-permission android:name="android.permission.INTERNET"/>

private class Async extends android.os.AsyncTask{
  @Override  
  protected Object doInBackground(Object... arg) {
    //Path 
    //android.os.Environment.getDataDirectory().getAbsolutePath()
    //		+ "/data/" + "com.example.fapp" + ""
    //DB4O Code here 
    return null;
  }
}

new Async().execute(null);

ObjectContainer db = Db4oEmbedded.openFile(Db4oEmbedded
				.newConfiguration(), DB4OFILENAME);

ServerConfiguration config = Db4oClientServer.newServerConfiguration();
//https://iboxdb.github.io/db4o-gpl-doc/javadoc/com/db4o/config/CommonConfiguration.html#updateDepth(int)
config.common().objectClass(Car.class).updateDepth(5);
//https://iboxdb.github.io/db4o-gpl-doc/javadoc/com/db4o/cs/Db4oClientServer.html#openServer(com.db4o.cs.config.ServerConfiguration,java.lang.String,int)
//Set Port = 0
ObjectServer server = Db4oClientServer.openServer(config, DB4OFILENAME, 0);
try {
  ObjectContainer client = server.openClient();
  // Do something with this clients
  client.close();
} finally {
  server.close();
}
//Open new Client for every request. Concurrent
public static void queryLocalServer(ObjectServer server) {
  ObjectContainer client = server.openClient();
  listResult(client.queryByExample(new Car("885588")));
  client.close();
}

//set PORT > 0
ObjectServer server = Db4oClientServer.openServer(Db4oClientServer
				.newServerConfiguration(), DB4OFILENAME, PORT);
server.grantAccess(USER, PASSWORD);
try {
  ObjectContainer client = Db4oClientServer.openClient(
    Db4oClientServer.newClientConfiguration(), "localhost",PORT, USER, PASSWORD);
  // Do something with this client, or open more clients
  client.close();
} finally {
  server.close();
}

var rs = see.query((Record r) -> r.indexField == dv);

public class Node
{
  [Indexed]
  public String Name;
  public Node Left;
  public Node Right;
}
    
StringBuilder sb = new StringBuilder();
var path = Environment.GetFolderPath(Environment.SpecialFolder.Personal);
path = Path.Combine(path, "t.db");
File.Delete(path);

var cf = Db4oEmbedded.NewConfiguration();
cf.Common.Add(new TransparentActivationSupport());
cf.Common.Add(new TransparentPersistenceSupport());
using (var oc = Db4oEmbedded.OpenFile(cf, path))
{
    using (var ss = oc.Ext().OpenSession())
    {
        Node root = new Node();
        root.Name = "Root";
        root.Left = new Node();
        root.Left.Name = "LEFT";
        root.Left.Left = new Node();
        root.Left.Left.Name = "LEFT.LEFT";
        ss.Store(root);
        ss.Commit();
    }
    using (var ss = oc.Ext().OpenSession())
    {
        sb.AppendLine(ss.QueryByExample(new Node { Name = "Root" }).First().Left.Left.Name);
    }
}

build 'db4o.j/db4o-core' project, get db4o-core.jar
use NetBeans open db4o-gpl/admins/om.j/ObjectManager/ 
build and run

Db4o-Projects/*/dotnet publish -c Release, get db4o DLLs
use MonoDevelop open  db4o-gpl/admins/om.net/OMAddin-2010.sln 
build and run

db4o

With regret we have to announce that Actian decided not to actively pursue and promote the commercial db4o product offering for new customers any longer.

Since the db4o dual licensing model allows for the free usage of the community edition of db4o for non-commercial purposes, 
you have the opportunity to continue to use it for your non-commercial applications or
even fork it to provide support for the community.
You can find the latest installer packages including the source tarball here for Java, .NET35, .NET40

Actian will continue to provide commercial licenses and support for existing customers with active support contract.