Compositor is a free, open-source, layer-based image editor for macOS, written in Swift and built around a Photoshop-style compositing workflow. Its author says he made it because Photoshop costs too much and GIMP never felt familiar enough to stay in flow. It is aimed at photographers, retouchers and designers on a Mac who want layers, masks, adjustments and blend modes in a native app, and at developers willing to open the Xcode project and bend a feature to their own workflow.
What it does
The README describes a feature set borrowed closely from Photoshop's compositing and post-processing side:
- Layers and folders with opacity and what the author calls Photoshop's full set of blend modes in the same order; a folder's opacity dims everything inside it.
- Layer masks you can paint, fill, invert, blur and feather anywhere on the canvas, including past the layer's own pixels; unlink a mask to transform it alone. Clipping masks and folder masks too.
- Adjustment layers: Hue/Saturation, Levels, Curves, Exposure, Gradient Map, Grain, Black and White, Color Balance, Invert, Gaussian Blur, Motion Blur and Noise.
- Layer effects — Stroke, Drop Shadow, Color Overlay, Inner Shadow, Outer Glow and Inner Glow — rendered on the GPU and editable at any time.
- Merge Down, Merge Layers and Merge Group, inline renaming, drag-and-drop reordering and nesting, Option-drag to duplicate, and copy-paste of whole layers and folders between projects.
- Non-destructive move, scale, rotate and flip, so an image keeps its full resolution however small you shrink it, plus free distort by Command-dragging a handle.
The project's own video mentions two things the saved README is cut off before reaching: real selections and content-aware fill. Treat the list above as the documented part, not the whole app.
How it works
Compositor is a native Mac app, not a cross-platform port, which is why its effects run on the GPU and its editing model stays non-destructive instead of baking transforms into pixels.
The detail most likely to interest technical readers is the file format. A project is a folder of PNG layers plus a manifest. That is the author's stated reason for claiming AI agents can edit a project directly: an agent needs no plugin API, it just writes PNGs and edits a text manifest on disk. No model, agent or API key ships with the editor — any agent you point at a project is your own, and you pay for it separately. The editor itself is a local app, with no cloud service named in the materials.
The code is MIT licensed and distributed as an Xcode project, so changing a feature is part of the pitch rather than a side effect.
Getting started
Requirements are strict: it runs only on Apple silicon Macs with macOS 26. Intel Macs are out, and so are Windows and Linux. No memory, disk or GPU figures appear anywhere in the material.
Nothing costs money. No subscription, no account and no paid service is named anywhere in the project.
There are three ways to install it. The one-line route is Homebrew:
brew install --cask robbietilton-compositor
Otherwise take the build from GitHub Releases at github.com/robbietilton/Compositor/releases/latest, or from the author's page at robbietilton.com/compositor. To modify it, clone github.com/robbietilton/Compositor and open the Xcode project.
When to use it / when not
The catch is the platform floor: an Apple silicon Mac on macOS 26 is a narrow target that excludes a large share of working machines.
Use it instead of Photoshop when your work is compositing and post-processing, your Mac is new enough, and the recurring licence is what stands in your way. Use it instead of GIMP when GIMP's interface and shortcut habits are what break your flow — Compositor deliberately mirrors Photoshop's layer model, blend-mode order and key commands.
Don't use it if you need prepress and CMYK, vector type, plugin compatibility or an Adobe round-trip, none of which the material claims. Don't use it if your team shares files across Windows or older Macs, and don't build a deadline around it yet: the repository's first commits are from September 2026, so this is a young project despite roughly 12,600 stars and 1,100 forks.
Alternatives
The two the materials name are the ones readers already know: Adobe Photoshop, which Compositor is openly modelled on and priced against, and GIMP, which is also free and open source and runs on Windows and Linux too. Off Apple silicon, GIMP stays the practical option.
Compositor deserves attention from any Mac photographer or designer who edits in layers and resents the subscription, and from Swift developers who want a substantial image-editing codebase to read or extend. The feature list is unusually complete for a project this young, and the folder-of-PNGs format makes scripted and agent-driven edits trivial. What should hold you back is not the ambition but the reach: until you are on an Apple silicon Mac running macOS 26, none of it is available to you, and until the project has more months behind it, keep a copy of your originals.