You will find, on this website, system utilities for macOS (OnyX, Maintenance, and Deeper). They are gratis, freely usable, and no registration is necessary. You may download, copy, and distribute them at no charge; however, you may not modify the software for distribution. You can use them for as long a time as you want.
OnyX is the main application. The Maintenance and Deeper applications are parts of OnyX.
Then if you use OnyX, the Maintenance and the Deeper applications are redundant!
OnyX is a multifunction utility for macOS which you can use to verify the startup disk and the structure of its system files, to run miscellaneous tasks of cleaning and system maintenance, to configure some hidden parameters of many of Apple’s applications, and more.
Maintenance is a system maintenance and cleaning utility for macOS which you can use to run miscellaneous tasks of system maintenance: run periodic scripts, rebuild the databases, delete application, font, and system caches, and more.
Deeper is a personalization utility for macOS which you can use to enable and disable the hidden functions of the Finder, Dock, Safari, iTunes, login window, and many of Apple’s applications, and more.