OnyX

OnyX has sat in Mac power users' Applications folders since 2003, and one developer, Joël Barrière, still ships it. It does two useful things. It runs maintenance — clearing caches selectively, rebuilding Spotlight and Launch Services databases, verifying the system file structure, deleting files the Finder refuses to move. And it gives you a real interface for the hidden Finder, Dock and Safari preferences you would otherwise set with defaults write commands copied off a blog post.

The price is nothing. Barrière accepts donations and has never sold a licence, which is why OnyX keeps turning up as the answer when somebody is about to pay for a Mac cleaner.

The thing to get right is the download. There is a separate OnyX for every major macOS release, and the site is blunt about not pointing an older build at a newer system — that is the one way this app can actually hurt you. The current 5.1.0 release wants macOS 27 on Apple silicon; older systems have their own builds further down the page.

Do not come for the promise of a faster Mac. Most of what the maintenance tab offers is unnecessary now, and clearing caches almost never fixes what people think it will. Come for the hidden-settings panel and the stubborn-file deletion, and treat the rest as occasionally handy.