DotNetBrowser

As a regular WinForms control, the BrowserView implementation provided in DotNetBrowser is compatible with ExcelDNA library. 

The following sample code demonstrates how to add DotNetBrowser in Excel Add-Ins using ExcelDNA:

C#

using System.Runtime.InteropServices;
using System.Windows.Forms;
using ExcelDna.Integration.CustomUI;
using DotNetBrowser;
using DotNetBrowser.WinForms;

namespace DotNetBrowserTab
{
    [ComVisible(true)]
    public class RibbonController : ExcelRibbon
    {
        public override string GetCustomUI(string RibbonID)
        {
            return @"
            <customUI xmlns='http://schemas.microsoft.com/office/2006/01/customui'>
              <ribbon>
                <tabs>
                  <tab id='dotnetbrowser_tab' label='DotNetBrowser Tab'>
                    <group id='dotnetbrowser_group' label='DotNetBrowser Group'>
                      <button id='dotnetbrowser_open' label='Open DotNetBrowser' 
                        onAction='OnShowCTP'/>
                      <button id='dotnetbrowser_close' label='Close DotNetBrowser' 
                        onAction='OnDeleteCTP'/>
                    </group >
                  </tab>
                </tabs>
              </ribbon>
            </customUI>";
        }

        public void OnShowCTP(IRibbonControl control)
        {
            CTPManager.ShowCTP();
        }


        public void OnDeleteCTP(IRibbonControl control)
        {
            CTPManager.DeleteCTP();
        }
    }

    /////////////// Define the UserControl to display on the CTP ///////////////////////////
    // Would need to be marked with [ComVisible(true)] if in a project
    // that is marked as [assembly:ComVisible(false)] which is the default for VS projects.
    [ComVisible(true)]
    public class DotNetBrowserControl : UserControl
    {
        public BrowserView browserView;

        public DotNetBrowserControl()
        {
            browserView = new WinFormsBrowserView();
            browserView.Browser.LoadURL("www.teamdev.com/dotnetbrowser");
            Controls.Add((Control)browserView);
        }

        //Ovverrided for focus
        protected override void WndProc(ref Message m)
        {
            if (m.Msg == 528 && !Focus())
            {
                //Set this property only for heavyweight render mode
                browserView.Focused = true;
                Focus();
            }
            base.WndProc(ref m);
        }
    }

    /////////////// Helper class to manage CTP ///////////////////////////
    internal static class CTPManager
    {
        static CustomTaskPane ctp;

        public static void ShowCTP()
        {
            if (ctp == null)
            {

                // Make a new one using ExcelDna.Integration.CustomUI.CustomTaskPaneFactory 
                ctp = CustomTaskPaneFactory.CreateCustomTaskPane(typeof(DotNetBrowserControl),
                    "DotNetBrowser");
                ctp.Visible = true;
                ctp.DockPosition = MsoCTPDockPosition.msoCTPDockPositionRight;
            }
            else
            {
                // Just show it again
                ctp.Visible = true;
            }
        }

        public static void DeleteCTP()
        {
            if (ctp != null)
            {
                // Could hide instead, by calling ctp.Visible = false;
                ctp.Delete();
                ctp = null;
            }
        }
    }
}

VB.NET

Imports System.Runtime.InteropServices
Imports System.Windows.Forms
Imports ExcelDna.Integration.CustomUI
Imports DotNetBrowser
Imports DotNetBrowser.WinForms

Namespace DotNetBrowserTab
    <ComVisible(True)>
    Public Class RibbonController
        Inherits ExcelRibbon

        Public Overrides Function GetCustomUI(ByVal RibbonID As String) As String
            Return _
                "
            <customUI xmlns='http://schemas.microsoft.com/office/2006/01/customui'>
              <ribbon>
                <tabs>
                  <tab id='dotnetbrowser_tab' label='DotNetBrowser Tab'>
                    <group id='dotnetbrowser_group' label='DotNetBrowser Group'>
                      <button id='dotnetbrowser_open' label='Open DotNetBrowser' 
                        onAction='OnShowCTP'/>
                      <button id='dotnetbrowser_close' label='Close DotNetBrowser' 
                        onAction='OnDeleteCTP'/>
                    </group >
                  </tab>
                </tabs>
              </ribbon>
            </customUI>"
        End Function

        Public Sub OnShowCTP(ByVal control As IRibbonControl)
            CTPManager.ShowCTP()
        End Sub

        Public Sub OnDeleteCTP(ByVal control As IRibbonControl)
            CTPManager.DeleteCTP()
        End Sub
    End Class

    <ComVisible(True)>
    Public Class DotNetBrowserControl
        Inherits UserControl

        Public browserView As BrowserView

        Public Sub New()
            browserView = New WinFormsBrowserView()
            browserView.Browser.LoadURL("www.teamdev.com/dotnetbrowser")
            Controls.Add(CType(browserView, Control))
        End Sub

        Protected Overrides Sub WndProc(ByRef m As Message)
            If m.Msg = 528 AndAlso Not Focus() Then
                browserView.Focused = True
                Focus()
            End If

            MyBase.WndProc(m)
        End Sub
    End Class

    Friend Module CTPManager
        Shared ctp As CustomTaskPane

        Sub ShowCTP()
            If ctp Is Nothing Then
                ctp = CustomTaskPaneFactory.CreateCustomTaskPane(GetType(DotNetBrowserControl), "DotNetBrowser")
                ctp.Visible = True
                ctp.DockPosition = MsoCTPDockPosition.msoCTPDockPositionRight
            Else
                ctp.Visible = True
            End If
        End Sub

        Sub DeleteCTP()
            If ctp IsNot Nothing Then
                ctp.Delete()
                ctp = Nothing
            End If
        End Sub
    End Module
End Namespace