// Сборка AntCore.dll (для совместного использования приложением и плагинами)
using System;

namespace Ant.Core
{
    [Serializable]
    [AttributeUsage(AttributeTargets.Class)]
    public sealed class CommandIdAttribute: Attribute
    {
        public CommandIdAttribute(string guid)
        {
            Id = Guid.Parse(guid);
        }

        public Guid Id { get; }
    }
}

// Сборка AntPluginExample1.dll
using System;
using System.Threading;
using Ant.Core;
using static System.Console;
namespace AntPluginExample1
{
    [Serializable]
    [CommandId("{382F5A14-9A96-4A05-80B3-10FE170B59DE}")]
    public sealed class HelloWorld : MarshalByRefObject, ICommand
    {
        public void Dispose()
        {
            WriteLine("Command disposed");
        }

        public void Execute()
        {
            WriteLine($"Domain: {Thread.GetDomain().FriendlyName}");
        }
    }
}

// Приложение, загружающее каждый плагин в свой AppDomain 
// и использующий его команды.
using System;
using System.Linq;
using System.Threading;
using Ant.Core;
using static System.Console;

namespace Ant.CLI
{
    class Program
    {
        static void Main(string[] args)
        {
            Title = "Ant CLI";
            WriteLine($"Current domain: {Thread.GetDomain().FriendlyName}");
            var domain = AppDomain.CreateDomain("AD #2", null, null);
            using (var command = (ICommand)domain.CreateInstanceAndUnwrap(
                "AntPluginExample1, version=1.0.0, culture=neutral, PublickKeyTocken=null",
                "AntPluginExample1.HelloWorld"))
            {
                command.Execute();
                var t = command.GetType();
                WriteLine($"command type: {t}");
                WriteLine("Attributes:");
                foreach(var att in t.CustomAttributes)
                {
                    WriteLine($"\t{att.AttributeType.Name}");
                }
            }
            AppDomain.Unload(domain);
            WriteLine("Press ENTER for exit...");
            ReadKey();
        }
    }
}

Current domain: AntCLI.exe
Domain: AD #2
command type: AntPluginExample1.HelloWorld
Attributes:
        SerializableAttribute
Command disposed
Press ENTER for exit...

SerializableAttribute
        CommandIdAttribute

using System;
using System.Threading;
using Ant.Core;
using System.Linq;
using static System.Console;
using System.Reflection;

namespace Ant.CLI {
    class Program {
        static void Main(string[] args) {
            Title = "Ant CLI";
            var currentMethodName = MethodBase.GetCurrentMethod().Name;

            WriteLine($"Method: {currentMethodName} is working in the " +
                $"'{Thread.GetDomain().FriendlyName}' domain.");

            var domain = AppDomain.CreateDomain("AppDomain #2", null, null);
            var asm = domain.Load("AntPluginExample1, version=1.0.0, " +
                "culture=neutral, PublickKeyTocken=null");
            var cmdInterfaceName = "Ant.Core.ICommand";

            foreach (var tc in asm.ExportedTypes.Where(
                n => n.IsClass && !n.IsAbstract &&
                null != n.GetInterface(cmdInterfaceName))) {
                using (var command = (ICommand)domain.CreateInstanceAndUnwrap(
                        asm.FullName, tc.FullName)) {
                    var t = command.GetType();
                    var cmdAttrib = Attribute.GetCustomAttribute(t,
                        typeof(CommandAttribute)) as CommandAttribute;
                    WriteLine($"Class '{t}':");
                    WriteLine($"\tCommand id: {cmdAttrib.Id}");
                    WriteLine($"\tCommand logical name: {cmdAttrib.LogicalName}");
                    command.Execute();
                }
            }
            AppDomain.Unload(domain);
            WriteLine("Press ENTER for exit...");
            ReadKey();
        }
    }
}