I'm looking for a very lightweight remote server monitor that can send
me text messages when various services fail.  The emphasis here is on
"lightweight".

Basically, I want something that is very easy to configure that can just
sit in the background and keep track of a remote email server (sending
and receiving email) and a few web sites.  If any of them go down for
more than a few minutes, I want the system to notify me.  I don't care
about web interfaces or graphs or anything like that.  Just "system down
== send kurt SMS message".

I'm pretty sure that Nagios can do that.  But I want a delicate tack
hammer here and Nagios is more of a hyper automated multi-headed
sledgehammer.

Bonus points if the tool can run on my WRT :-)

Any leads?

Kurt