All that have to be done is in global.asax file:
Sub Application_Start(ByVal sender As Object, ByVal e As EventArgs)
Application(
"OnlineUsers") = 0
End Sub
Sub Application_End(ByVal sender As Object, ByVal e As EventArgs)
End Sub
Sub Application_Error(ByVal sender As Object, ByVal e As EventArgs)
End Sub
Sub Session_Start(ByVal sender As Object, ByVal e As EventArgs)
Application.Lock()
Application("OnlineUsers") = CInt(Application("OnlineUsers")) + 1
Application.UnLock()
End Sub
Sub Session_End(ByVal sender As Object, ByVal e As EventArgs)
Application.Lock()
Application("OnlineUsers") = CInt(Application("OnlineUsers")) - 1
Application.UnLock()
End Sub
And to get the counter value in any form you want just call Response.Write(Application("OnlineUsers")) or Label1.Text = Application("OnlineUsers") whatever you feel comfortable.
It will show all open sessions.
Application.Lock() is used to lock down the application state values for editing only from one person at a time and Application.UnLock() is unlocking the state for edit from somebody else.
Hope it helps