John's Background Switcher is described as 'John’s Background Switcher (or JBS for short) periodically changes the wallpaper on your computer (like every hour or every day) to something interesting. JBS sits in your system tray (down by the clock) and changes your background at the time interval of your choosing' and is a popular Wallpapers Hub in the photos & graphics category. There are more than 25 alternatives to John's Background Switcher for a variety of platforms, including Windows, Mac, Linux, Web-based and Android apps. The best John's Background Switcher alternative is Variety Wallpaper Changer, which is both free and Open Source. Other great apps like John's Background Switcher are Muzei, Wallpaper Wizard, Irvue and Splashify.
This is the one! Free, no bull and the randomizer actually allows you to say to yourself: "Oh, I haven't seen this one since I added it to my gallery! I knew I had it in my gallery!" It uses a way better randomizer unlike many others (including Window's built-in bs) that just repeat the images depending on the cheap time of day randomizing algo. This is a must have tool.