Boost

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

If you have looked at CleanMyMac, iStat Menus or AppCleaner and did not want a subscription, this covers the parts most people actually use.

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

Or build it yourself, which takes about as long and involves no Gatekeeper at all:

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

macOS 14 or later, Apple Silicon and Intel, one universal binary. It builds with Command Line Tools, so Xcode is not required. If Boost is useful to you, a star helps other people find it.

On signing. 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 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.

boost-ad-x.mp4

What you get

A menu bar popover. Click the icon and you see memory pressure, a short graph, swap, how much is cached and compressed, and the five apps using the most memory. Point at one to pause or quit it. Free Memory is one click away, and free disk space sits at the bottom. The icon shows a number only when memory is getting busy, or always if you turn that on.

History. Boost records a reading every minute and keeps a week. The Memory tab charts it over 2 hours, 24 hours or 7 days, with the peak, the average and how many times your Mac went into swap. That answers "was it slow at 3pm yesterday" instead of leaving you to guess.

Pause apps instead of quitting them. Pause freezes an app and its helpers. It uses no CPU, keeps its state, and comes back exactly where it was. Pick apps to pause automatically after they sit in the background for 5 to 60 minutes. Boost wakes each one the moment you switch to it. If Boost crashes or is killed, a small watchdog resumes everything it froze, so nothing stays frozen.

Alerts that mean something. Boost can tell you when swap passes 1, 2 or 4 GB, and when memory has stayed tight for a full minute, naming the app using the most. A spike that passes on its own is ignored.

Disk cleanup that refuses the risky parts. It finds caches that the tool that made them will rebuild: Homebrew, npm, pip, uv, Cargo, Gradle, Xcode DerivedData, simulator caches, app caches, logs. It will not touch Downloads, node_modules found by name, or iOS backups.

Projects. Finds node_modules, Rust target, SwiftPM .build, Python virtualenvs, CocoaPods and similar folders in projects you have not touched for 30 to 180 days. A folder is listed only when the manifest next to it proves what it is. Everything goes to the Trash.

Uninstall. Pick an app, or drop one onto the window, and Boost lists what it left in your Library with sizes before anything moves. Only exact matches are listed. Everything goes to the Trash, and there is an Undo.

The small things. Start at login. A Dock badge. An optional global shortcut (⌥⌘B). Sort by name, memory or CPU. Reveal in Finder. Light and dark mode.

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.
• Projects and Uninstall move things to the Trash, so you can put them back. The Disk tab deletes, and says so on screen.
• 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.

How Free Memory works

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.

Permissions

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.

Command line

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 testing

./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.

To regenerate the screenshots in this README from the real views:

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

Is it 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. See the rules written into Pro.swift.

Licence

GPL-3.0. See LICENSE.

Built by Karim Masmoudi. My other projects are at karimmasmoudi.vercel.app.