[hanru]

On Windows 7 and later, the system will automatically detect network connectivity and alert user if there's no internet access. I've spent some time on learning how this works, and here is the technical detail: http://blog.superuser.com/2011/05/16/windows-7-network-aware...

I wonder why OS X doesn't have such a useful functionality...

[sirn]

In OSX, there is a "Alert: No Internet Connection" notification directly in the AirPort menu bar[1] when there is no internet connection.

[1]: http://d.pr/i/yjvG

[dpedu]

This doesn't appear nearly as quickly as the software in OP's post would.