Install-Package Syncfusion.SfDiagram.WPF

xmlns:syncfusion="http://schemas.syncfusion.com/wpf"

<Window xmlns:syncfusion="http://schemas.syncfusion.com/wpf" ...>
    <Grid>
        <syncfusion:SfDiagram x:Name="diagram">
            <syncfusion:SfDiagram.Nodes>
                <syncfusion:NodeCollection/>
            </syncfusion:SfDiagram.Nodes>
            <syncfusion:SfDiagram.Connectors>
                <syncfusion:ConnectorCollection/>
            </syncfusion:SfDiagram.Connectors>
        </syncfusion:SfDiagram>
    </Grid>
</Window>

using Syncfusion.UI.Xaml.Diagram;

// Add nodes
var node1 = new NodeViewModel { ID = "Start", UnitWidth = 120, UnitHeight = 40,
    OffsetX = 200, OffsetY = 100, Shape = this.Resources["Ellipse"] };
var node2 = new NodeViewModel { ID = "End", UnitWidth = 120, UnitHeight = 40,
    OffsetX = 200, OffsetY = 250, Shape = this.Resources["Rectangle"] };
(diagram.Nodes as NodeCollection).Add(node1);
(diagram.Nodes as NodeCollection).Add(node2);

// Add connector
var connector = new ConnectorViewModel { SourceNodeID = "Start", TargetNodeID = "End" };
(diagram.Connectors as ConnectorCollection).Add(connector);