If you’ve upgraded to macOS Mojave (10.14) and been disappointed that your collection of .qtz screen savers stopped working, it’s good to know that you can get them working again for just a few dollars.
The app you’ll need is called Backgrounds, and it’s on the Mac App Store. This app lets you use Quartz Composer files as not only screen savers, but as desktop wallpaper as well. The developer has been responsive by email, and I’ve not had any problems.
Note: This is not a paid post! Also, a competing app (Mach Desktop 4K) claimed to do the same thing, but didn’t work properly for me.