The 1.1 version of RainingCubes for Mac was available to download on the developer's website when we last checked. We cannot confirm if there is a free download of this app available.
Please check the Mac app with an antivirus before launch as it is downloaded from the developer's website, and we cannot ensure that it is safe. The program lies within Theming Tools, more precisely Screensavers. The actual developer of this free software for Mac is Nick Zitzmann.
From the developer:
RainingCubes is a screen saver for OS X that animates anywhere from one to thousands of multi-colored cubes doing what cubes do when they have no surface beneath them, and the force of gravity is applied to them.
That might not be too interesting on its own, but RainingCubes is the first screen saver for OS X that does its drawing using the new Metal 3D drawing API in OS X 10.11 (El Capitan).
You may want to check out more Mac applications, such as scarytime v9, System47 or DesktopEarth 3D, which might be related to RainingCubes.