Create a custom Node for Node Editor Winforms: https://github.com/komorra/NodeEditorWinforms

NodeString.cs

[Serializable]
[TypeConverter(typeof(ExpandableObjectConverter))]
public class NodeString : ISerializable
{
    [DisplayName("Input")]
    public string SetValue { get; set; }

    public override string ToString()
    {
        return "String";
    }

    //NodeContext ctor
    public NodeString() { }

    public NodeString(string value)
    {
        SetValue = value;
    }

    private NodeString(SerializationInfo info, StreamingContext ctx)
    {
        foreach (SerializationEntry entry in info)
        {
            switch (entry.Name)
            {
                case "NodeString":
                    SetValue = info.GetString("NodeString"); break;
            }
        }
    }

    public void GetObjectData(SerializationInfo info, StreamingContext context)
    {
        if (!string.IsNullOrEmpty(SetValue)) info.AddValue("NodeString", SetValue);
    }
}