Boost

A free, open source Mac app for memory and disk space.
It lives in your menu bar, shows what is really using your RAM, pauses apps you are not using, and finds what is safe to remove.

Website  ·  Download  ·  Guides  ·  Report a bug

If you looked at CleanMyMac, iStat Menus or AppCleaner and did not want a subscription, Boost covers the parts most people actually use. No account, no analytics, no network access of any kind.

Install

brew install --cask kernel-hunter/boost/boost

Or build it yourself. It takes about as long and involves no Gatekeeper at all:

git clone https://github.com/Kernel-Hunter/boost.git
cd boost && ./Scripts/build.sh

Needs macOS 14 or later. One universal binary for Apple Silicon and Intel. It builds with the Command Line Tools, so Xcode is not required.

About signing and Gatekeeper

Boost is signed with a local certificate, not notarized, because notarizing needs a paid Apple Developer account. A downloaded .zip will be stopped by Gatekeeper the first time. The Homebrew cask clears the quarantine flag for you, and building from source never sets one, so use one of those two.

If you downloaded the zip anyway: on macOS 14, right-click the app and choose Open. On macOS 15 and later, open it once, then go to System Settings, Privacy & Security, and click Open Anyway next to the message about Boost.

What it does

Menu bar popover	Memory pressure, a short graph, swap, cached and compressed memory, and the five apps using the most. Point at one to pause or quit it. Free Memory is one click away.
A week of history	One reading a minute for seven days. Chart it over 2 hours, 24 hours or 7 days, with the peak, the average and how often your Mac went into swap.
Pause, not quit	Freezes an app and its helpers. No CPU, state kept, resumes exactly where it was. Pause apps automatically after 5 to 60 minutes in the background.
Alerts that mean something	A notification when swap passes 1, 2 or 4 GB, or memory stays tight for a full minute. It names the app using the most. Brief spikes are ignored.
Disk	Caches the owning tool rebuilds: Homebrew, npm, pip, Cargo, Gradle, Xcode DerivedData and device support, simulators, app caches, logs. Docker's disk image is shown with the command to shrink it, never deleted.
Projects	Old node_modules, Rust target, SwiftPM .build, virtualenvs and CocoaPods in projects you have not touched for 30 to 180 days.
Large Files	The biggest files in Downloads, Desktop, Documents, Movies, Music and Pictures, with when you last opened each.
AI Models	Models that Ollama, Hugging Face and LM Studio downloaded, with sizes. Ollama models share files, so each size is what removing that one frees.
Uninstall	Pick an app or drop one on the window. Leftovers in your Library are listed with sizes before anything moves, with an Undo.
Copy Report	A plain text summary for a bug report: your Mac, pressure, swap, biggest apps. App names and sizes only, no file paths, nothing sent anywhere.

Also: start at login, a Dock badge, an optional global shortcut (⌥⌘B), light and dark mode, and Liquid Glass on macOS 26. Older systems get a plain material look.

Screenshots

Disk: nothing is ticked for you	AI Models: what removing each one frees
Uninstall: leftovers listed before anything moves	Menu bar popover

boost-ad-x.mp4

Why it is built this way

Most Mac cleaners show you a big number and offer to make it smaller. The number is usually cached memory, which macOS is using well, and shrinking it makes your Mac slower. Boost does the opposite on purpose.

• It tells you when there is nothing to do. If swap is at zero, the header says your Mac is coping.
• It explains a figure before offering to change it. Cached memory is shown as available, because it is.
• Nothing is ticked for you. Removing files should be a decision.
• Almost everything goes to the Trash, so you can put it back. Only the caches in the Disk tab are deleted, and the screen says so.
• Two safety layers guard deletion. An allowlist of what may be scanned, and a second check of the resolved path right before each removal. A symlink in a cache that points at your documents is how tools like this destroy data, and there is a test that builds exactly that trap.

New to the topic? The guides explain memory pressure, cached memory, System Data and how to uninstall an app completely, with or without Boost.

FAQ

Does Free Memory actually work?

Windows tools like Mem Reduct call EmptyWorkingSet, which lets one process push another process's pages to the pagefile. macOS has no public equivalent, as Apple's kernel source shows. It also would not help. macOS compresses memory instead of swapping early, and reading a compressed page from RAM is much faster than reading it back from an SSD.

So Boost uses what macOS does offer. It asks the system for memory through Apple's own memory_pressure tool, which nudges the kernel to release idle pages and compress what it can. Then it checks the readings before and after and reports only what actually stopped being used. It does not close apps, delete files or ask for a password, and it stops early if swap starts growing.

Expect a few hundred MB to around a gigabyte on a typical run. If your Mac is not short on memory, there is little sitting idle to give back. Settings has an aggressive mode that asks harder. It is off by default and warns you why: pushed far enough, the kernel may kill something on its own.

What permissions does it need?

What	Why	When
None	Reading the process table and memory stats, and signalling your own apps	Always
Accessibility	Counting an app's open windows	Only for "close button quits the app"
Notifications	The swap and pressure alerts	Only if you turn them on
Login item	Starting Boost at login	Only if you turn it on
Admin password	/usr/sbin/purge	Only if you turn on the optional disk cache purge

No analytics, no telemetry, no update check, no network access of any kind. There is nothing to opt out of. See SECURITY.md.

Is it safe to pause an app?

Pause sends the app and its helpers SIGSTOP, and resuming sends SIGCONT. Boost writes what it froze to a lease file and runs a small watchdog, so if Boost crashes or is killed, everything it froze is resumed. It never pauses itself, and an alert can pause apps you ticked but cannot close them.

Is it really free?

Yes, and the parts that matter always will be. Safety, honest readings and anything that already shipped free are not going behind a paywall. The rules are written into Pro.swift.

Is there a command line version?

boost.sh does the same job headlessly, for a hotkey or a script:

./boost.sh              # close apps and helpers
./boost.sh --pause      # freeze them instead
./boost.sh --resume     # unfreeze everything, system-wide
./boost.sh --dry-run    # show what it would touch, change nothing

Pins made in the app are written to ~/Library/Application Support/Boost/keep.txt, and the script reads the same file.

Building and contributing

./Scripts/build.sh          # build and install to /Applications
./Scripts/test.sh           # run the suite

Use Scripts/test.sh rather than swift test. See CONTRIBUTING.md for the two flags it needs and why their error messages blame the wrong thing. Issues and pull requests are welcome. The bug report form asks for a Copy Report from the popover, which makes memory problems much easier to track down.

To regenerate the screenshots from the real views:

swift build && .build/debug/boost --snapshot docs/snapshots

License

GPL-3.0. See LICENSE.

Built by Karim Masmoudi. If Boost is useful to you, a star helps other people find it.