Monitorix is a free, open source, lightweight system monitoring tool designed
to monitor as many services and system resources as possible. It has been
created to be used under production UNIX/Linux servers, but due to its
simplicity and small size may also be used to monitor embedded devices as
well.

It mainly consists mainly of two programs: a collector, called monitorix, which
is a Perl daemon that is started automatically like any other system service,
and a CGI script called monitorix.cgi.

WWW: https://www.monitorix.org/