Mos is a free, open-source Mac utility that smooths and reverses scroll direction independently for third-party mice, fixing the jarring behaviour that plagues every non-Apple pointing device on macOS.
What is Mos?
Mos is a lightweight macOS system utility developed by Caldis that intercepts scroll events from USB and Bluetooth mice and reprocesses them with configurable easing and direction settings. Where macOS treats scroll wheel input as an afterthought for anything that isn't a Magic Mouse or trackpad, Mos steps in between the driver and the window server to give you butter-smooth, gliding momentum — without touching trackpad behaviour at all.
The project is open-source and freely downloadable from the developer's own site, with no account, no subscription, and no telemetry. It installs as a small menu-bar agent and asks for Accessibility permission, which it needs to intercept the scroll events at the system level.
What does Mos do best?
Mos excels at decoupling scroll direction and smoothness between your mouse and trackpad — something macOS categorically refuses to do in System Settings. Apple's "Scroll & Zoom" direction toggle applies globally; flip it for your Logitech MX Master and your trackpad scrolls backwards too. Mos surgically reverses the mouse wheel while leaving the trackpad exactly as it is.
Beyond direction, the smoothing engine is the star. You get a momentum curve you can tune with a simple slider: crank it up and you get the languid, physics-driven feel of a Magic Mouse; dial it down for a near-instant response that suits shooters and CAD work. Per-app scroll speed overrides let you set a different sensitivity inside Final Cut Pro versus Safari — a genuinely thoughtful touch I've come to rely on when switching between a video timeline and a long article.
- Independent scroll direction — mouse and trackpad flip independently at last
- Smooth momentum scrolling — configurable easing curve, not a binary on/off
- Per-application overrides — different speed and smoothing per app
- Extremely low overhead — runs as a menu-bar agent, negligible CPU and RAM
- Scroll event log — a live debug view shows raw vs processed events, useful for diagnosing driver conflicts
Is Mos free?
Yes — Mos is completely free to download and use. The developer accepts optional donations through the official site, but every feature, including per-app overrides and the advanced scroll curve settings, is available at no cost. There is no Pro tier and no feature gate.
Who should use Mos?
Mos is essential for anyone who uses a third-party scroll-wheel mouse on a Mac with any regularity. That covers a wide net: designers who keep a Logitech or Microsoft mouse docked to a studio iMac, developers whose wrists prefer a physical wheel to a trackpad after eight hours of scrolling through diffs, and gamers who want natural scrolling on a trackpad but Windows-style direction on a gaming mouse.
If you use only Apple hardware — Magic Mouse or trackpad — Mos has almost nothing to offer you. Apple's own input devices already get smooth scrolling from the OS. Mos exists precisely because third-party mice do not.
What are the best Mos alternatives?
The closest paid alternative is SteerMouse, a $20 driver replacement that goes further than Mos — it can remap buttons, adjust pointer acceleration curves, and set polling rates. If you need deep hardware-level control, SteerMouse earns its price. LinearMouse is another free, open-source option that overlaps with Mos significantly and adds pointer sensitivity controls that Mos lacks; it's a legitimate choice if you want everything in one free tool.
For scroll-specific smoothing without the direction problem, some users reach for Scroll Reverser (free, directionally focused) or rely on Logitech's own Logi Options+, which handles smoothing for Logitech mice only. Neither gives you the per-app granularity that Mos or LinearMouse offer.
I've kept Mos in my login items for over a year because it does its one job — smooth, correctly-directed scrolling — without the configuration overhead of SteerMouse or the occasional instability I've seen in beta builds of LinearMouse.
How does Mos compare to LinearMouse?
Mos and LinearMouse share the same core mission but diverge in scope. LinearMouse adds pointer speed and acceleration controls that Mos deliberately leaves out; it also supports disabling mouse acceleration entirely, which matters to FPS gamers. Mos, by contrast, keeps its UI minimal — one smoothing slider, one direction toggle, and a per-app list — making it faster to configure for casual users. Both are free and open-source. If you only want scroll smoothing and direction independence, Mos is the leaner pick; if you want a full input-remapping layer without paying for SteerMouse, LinearMouse is the broader tool.
