UsefulSaver is a screensaver with a difference. There's no slideshow, no flying objects, no fireworks, no graphics at all (not initially, anyway) - instead the program just displays useful and dynamically updated system information.
One pane reveals your CPU usage, memory consumption and battery life, for instance.
Another shows the activity on each of your hard drives.
A third displays the most active processes. Another shows your free disk space on each drive. And UsefulSaver also displays the time and date, just for good measure.
By default this is all fairly plain, however if you check the screensaver options then you'll be able to tweak your text colour, font, font size, background colours, borders and more.
And if your system has multiple monitors then the program can even display photos on them. The Options dialog and Help file will tell you more.