As with any other system indicator this will also let you graphically "see"....
*. CPU load.
*. RAM usage.
*. HDD usage.
*. Swap space related information.
*. Network... etc are among its main features.
You can also manually set its colors according to your preference as well. It actually looks very similar to the one that comes with Gnome desktop but since in Unity you can't use it... this will most definitely come in handy. The installation is also pretty simple. Just download your version (32/64-bit) from below and simply double click on it.