Monitorix

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 Linux/UNIX servers, but due to its simplicity and small size can be used on embedded devices as well. It 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. Monitorix includes its own HTTP server built in (which is listening by default on port 8080/TCP) to see the statistics graphs, so you aren't forced to install a third-party web server to use it. Just point your browser at http://localhost:8080/monitorix.