Observium CE it's just what I was looking, easy, simple.

I just miss alerting system (e-mail) when a node is down.

I read on wiki that new alerting system is not on CE (yet):

will be added sometimes or will be a "premium" feature?

For now I made a raw "alerting" system, modifying source code.

At includes/polling/functions.inc.php I added a small script
into poll_device function, just under status check.
It uses php-mail and sends me a message indicating
just hostname and status (Up or Down)

Obviously it's hardcoded, but it works for me.

Thanks for this nice software

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