I've been a member there (in active lately) for quite some time. I see now its got a "new" look. I know nothing about open source software thou, sorry. Just don't get it from cnet or softonic.
I used that when I had XP. With Win7, I find the build-in screensave/wallpaper setup do what I want...change wallpaper every so often and have a slideshow as screensaver. Anyway, have a look at the site below. Filter the results by license type, OS, etc.