In MAA on "Webwork" server, I am using “webmin” tool, which is basically a GUI interface for Linux administration and it has different add-on modules. One of the add-on is “webmin system stats” for system performance / application monitoring.
Webminstats is a Webmin's module which display a graphical log of historic information. It's modular in design, as to be able to log everything from CPU usage to email box size.
URL for "Webmin" is http://www.webmin.com/
Tool "webmin system stats" can be downloaded http://sourceforge.net/projects/webminstats/