Not sure if this qualifies as an "app", but I wrote this little powershell script to test for an active internet connection. Beeps when connected. I use it almost every day, because my cable modem takes a variable length of time to boot up, and I got tired of checking manually

  $connected = $false
  while($true)
  {
   if (-not $connected)
   {
    $connected = Test-Connection www.google.com -Quiet
   }
   else
   {
    Write-Host "Connected"
    [console]::beep(1000, 500)
   }
   Start-Sleep -Seconds 2
  }