[CentOS] Recommendation On Ping And Alert Tool

A bit off topic, but I keep looking for an answer to this question and
coming up with nothing... so I thought I would go to the gurus. :-)
 Can anyone recommend a good package for pinging other devices and sending
an email/alert when they go down? I'm aware of all kinds of more complex
things with GUIs and a zillion other bells and whistles we aren't looking
for, but we just want a simple tool (could be daemon or something run from
cron) that runs every 1 - 5 minutes and alerts us when stuff disappears.
Would need some basic logic like only sending one email/alert when something
goes down (vs sending an email every 1-5 minutes until it comes back up).
:-) We need to avoid a requirement for an X-windows GUI, but a web-GUI would
probably be fine (a GUI-less command-line thing would probably be best).
 TIA,
KC
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