C#

using System;
using System.Collections.ObjectModel;
using System.Management.Automation;
using System.Management.Automation.Runspaces;
using Microsoft.Office.Interop.Excel;

namespace ConsoleApplication3
{
    class Program
    {
        static void Main()
        {
            Application app = new Application();
            app.Visible = true;
            app.Workbooks.Add(XlWBATemplate.xlWBATWorksheet);

            Runspace runspace = RunspaceFactory.CreateRunspace();
            runspace.Open();
            runspace.SessionStateProxy.SetVariable("Application", app);
            Console.WriteLine(app.Version);
            Pipeline pipeline = runspace.CreatePipeline("$Application");

            Collection<PSObject> results = null;
            try
            {
                results = pipeline.Invoke();
                foreach (PSObject pob in results)
                {
                    Console.WriteLine(pob);
                }
            }
            catch (RuntimeException re)
            {
                Console.WriteLine(re.GetType().Name);
                Console.WriteLine(re.Message);
            }
        }
    }
}

using System;
using System.Windows.Forms;
using System.Management.Automation;
using System.Management.Automation.Runspaces;
using System.Collections.ObjectModel;
using Microsoft.Office.Interop.Excel;

namespace POSHAddin
{
    public partial class POSHControl : UserControl
    {
        public POSHControl()
        {
            InitializeComponent();
        }
        private void btnRun_Click(object sender, EventArgs e)
        {
            txtOutput.Clear();

            Microsoft.Office.Interop.Excel.Application app =
                Globals.ThisAddIn.Application;

            Runspace runspace = RunspaceFactory.CreateRunspace();
            runspace.Open();
            runspace.SessionStateProxy.SetVariable("Application", app);

            Pipeline pipeline = runspace.CreatePipeline(
                "$Application | Get-Member | Out-String");
            app.ActiveCell.Value2 = "Test";

            Collection<PSObject> results = null;
            try
            {
                results = pipeline.Invoke();
                foreach (PSObject pob in results)
                {
                    txtOutput.Text += pob.ToString() + "-";
                }
            }
            catch (RuntimeException re)
            {
                txtOutput.Text += re.GetType().Name;
                txtOutput.Text += re.Message;
            }
        }
    }
}

TypeName: System.__ComObject 

Name                        MemberType   Definition 
----                        ----------   ---------- 
CreateObjRef                Method       System.Runtime.Remoting.ObjRef CreateObj... 
Equals                      Method       System.Boolean Equals(Object obj) 
GetHashCode                 Method       System.Int32 GetHashCode()
GetLifetimeService          Method       System.Object GetLifetimeService() 
GetType                     Method       System.Type GetType() 
InitializeLifetimeService   Method       System.Object InitializeLifetimeService() 
ToString                    Method       System.String ToString()