What do you use to monitor & alert when a device on the lan goes down?

I used to use Mortens Host Alive for the old XP days, even got it to work on Vista once, but now I need a new solution.

Basically we'd like a free/low cost tool that runs on a workstation/server and can send an email when another device on the lan goes offline.

It doesn't have to be fancy. We wanted to monitor some nas devices by ip address, servers, Barracuda, cctv dvr's etc...

Do any of ya'll have any ideas? I've been Goggling myself silly and coming up empty. Thanks!