Project1.Log.Write("1");
Project2.Log.Write("2");
Project1.Log.Write("3");

public static class Log
{
    private static readonly Lazy<Logger> Logger = new Lazy<Logger>(CreateLogger);

    private static Logger CreateLogger()
    {
        string assemblyFolder = Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location);
        LogManager.Configuration = new XmlLoggingConfiguration(assemblyFolder + "\ProjectX.exe.nlog", true); //X means project id
        return LogManager.GetCurrentClassLogger();
    }

    public static void Write(object log)
    {
        Logger.Value.Debug(log);
    }
}