XScreenSaver is a great collection of screensavers that will help you decorate your screen with a different theme every day. Once you install the application, a folder will be opened which contains all the available screensavers. The program doesn't have a user interface. You just need to select the screensaver you wish to use from the extensive list, click on it to install, and you will have it available in the System Preferences to use it whenever you want. There is no description of the screensavers, so you will just guide your choice with its name, or install it to see what it is about.
The screensavers are organized alphabetically by name and they include mazes, tunnels, clocks, galaxies, cubes and many other things. They are all digitally created, so most of them don't look very realistic. From the Preferences menu, you will be able to customize speed, thickness, and other features that are specific for the screensaver you have chosen.
All in all, if you are looking for an extensive list of free screensavers to decorate your screen with, XScreenSaver may be an excellent choice.