What is a macOS Overlay?

A macOS overlay is a visual layer that sits above other application windows, usually transparent so the apps beneath remain visible. Overlays are used to add information or emphasis on top of the screen: think of an annotation drawn over a slide, a spotlight around the cursor, or a heads-up display showing status. Because the overlay is its own layer, it can highlight content without modifying the underlying apps.

An overlay is different from an app that owns its own window content. It does not change or capture what is beneath it; it simply paints on top. Overlays typically stay above other windows (always-on-top) and pass interaction through where appropriate. This makes them well suited to presentations, recordings, and live demos where you want to draw attention to parts of the screen.

Limelight uses macOS overlay layering to paint a cursor spotlight, an on-screen keystroke display, and freehand drawing directly on top of whatever you are showing, while leaving your apps untouched. It then goes further than a pure overlay: it records your screen and exports a finished, cinematic video itself — auto-zooming on clicks and smoothing the cursor — with those on-screen aids baked into the file. Everything runs locally, so it uploads nothing.