I downloaded and installed the EKG Simulation EKS screensaver and the screen comes up, but it does absolutely nothing. Then it tells me that it's only a trial version? What? It said it was free when I downloaded it.
I've checked what you've said and it appears that EKG Simulation EKS - 1000 is indeed free to download, but the program's license is shareware which means that you can download it as a demo/trial and then have to purchase a license key in order to unlock it. This is specified on the official website of the developers found below.
Here is the official website: http://ekg.twobrotherssoftware.com/purchase.php