You have may used screensavers that display content from RSS feeds on your idle desktop but here’s something different.
Wikipedia Screensaver, as the name suggests, will load a random page from Wikipedia and display it on your idle desktop in full screen mode. The next web page (an article from Wikipedia again) will load after 30 seconds or you can configure the delay.
Wikipedia Screensaver is a free download for Windows only.
Related: Your Guide to Wikipedia Tools