If I want to monitor some machines that I'm not the primary maintainer of (ie, I don't have access to install packages), are there any lightweight alternatives to things like Nagios? I'm looking for a script (bash, Perl, PHP, etc.) that does basic monitoring of Linux servers and services (disk space, web server, maybe cpu usage, etc.) and sends alerts when necessary.
I've found a few one-off scripts, but I'm surprised there isn't something slightly more comprehensive.