Reproducing i3 on Mac: From Aerospace to Flashspace

If you've used i3 on Linux, you know the feeling. Workspaces bound to keys. Windows tile automatically. No animations, no transitions, no waiting. You press a key and you're there. Everything else feels slow after that.

When I moved to macOS full-time I wanted that back. This is the setup I landed on after trying several approaches — and the one thing I wish someone had told me earlier.

What i3 actually gives you

Before jumping into tools, it's worth naming what makes i3 great. It's not just tiling. Tiling is table stakes. The real value is:

Workspaces on a keybind. Super+1 takes you to workspace 1. Instantly. No animation, no slide.
Windows follow rules. Browser goes to workspace 2, terminal to workspace 1, Slack to workspace 4. You don't arrange anything manually.
Keyboard-first everything. Moving, resizing, focusing — all keys. The mouse is there if you need it, but you shouldn't.

The challenge on macOS is that Spaces exist but they're slow, animated, and not really designed for keyboard-driven workflows. Mission Control is a visual picker, not a workspace switcher.

The Aerospace phase

Aerospace was my first attempt. It's a tiling window manager for macOS inspired directly by i3³. Tree-based layouts, configurable keybindings, workspace support — the feature list reads like an i3 port.

And it works. The tiling is solid. You get i3-style layouts with tall, accordion, and manual splits. Config is a .toml file. The i3 mental model translates.

But I ran into friction:

Workspace switching felt heavy. Aerospace manages its own workspace abstraction on top of macOS Spaces. Switching between workspaces had a noticeable delay — not huge, but enough that it didn't feel like i3. On i3, workspace switching is instant. On Aerospace, there was a beat.

Conflicts with macOS. Aerospace fights the OS in subtle ways. Stage Manager, fullscreen apps, multi-monitor setups — things would occasionally break or behave unexpectedly. The tool is doing a lot of work to paper over the fact that macOS doesn't want to be a tiling WM.

More than I needed. I realized I don't actually need full i3-style tiling on Mac. Most of my work happens in a terminal and a browser. What I really needed was fast workspace switching and basic window placement — not a full tree-based layout engine.

Flashspace: the thing that clicked

Flashspace is a workspace manager for macOS. Not a tiling window manager — a workspace manager. The distinction matters⁵.

It maps keyboard shortcuts directly to macOS Spaces. Super+1 goes to Space 1. Super+2 goes to Space 2. No animation. No transition. It's instant in a way that macOS's built-in Space switching is not.

The first time I pressed a keybind and was just there — no slide, no fade, no delay — I knew this was it. That's the i3 feeling.

What Flashspace does

Instant workspace switching. This is the core feature and the reason to use it. It disables macOS's Space transition animations and maps each Space to a keyboard shortcut. The switch is effectively zero-latency.

App-to-workspace assignment. You can configure which apps belong to which Space. Browser on Space 2, terminal on Space 1, communication tools on Space 3. When you switch to a Space, the right apps are focused.

Per-workspace wallpapers. Minor but useful — each Space can have its own wallpaper. Visual distinction helps you orient instantly after switching.

Lightweight. Flashspace is a menu bar app. It doesn't manage window layouts, it doesn't override macOS window management, it doesn't fight the OS. It makes Spaces actually usable, and gets out of the way.

My setup

Here's my actual configuration:

Space 1 — Terminal. Ghostty, usually with multiple tmux sessions. This is where the actual work happens.

Space 2 — Browser. Firefox. Research, docs, PRs, deployed apps.

Space 3 — Communication. Slack, Discord, email. Isolated from work so it can't steal focus.

Space 4 — Misc. Finder, system preferences, whatever doesn't have a permanent home.

Keybindings:

Alt+1 through Alt+4 — switch to Space 1-4
Alt+Shift+1 through Alt+Shift+4 — move the focused window to that Space

That's the whole setup. Four workspaces, eight keybindings.

For tiling: pair it with a lightweight tiler

Flashspace handles workspaces but not window tiling. If you want windows to snap into place without dragging, pair it with macOS's native tiling (Sequoia added keyboard-driven tiling) or a lightweight tool like Loop for quick half-screen / quarter-screen snapping.

I use macOS native tiling for the simple cases (left half, right half) and that's enough. I don't need a tree-based layout engine — I need my terminal on the left and my browser on the right, and I need to switch workspaces instantly.

Why snappiness is the whole point

The temptation with window management tools is to chase features. More layout options, more rules, more automation. But the thing that makes i3 great isn't the feature set — it's the speed. You think "I need the browser" and the browser is there. No animation, no waiting, no context switch.

Aerospace has more features than Flashspace. It's closer to a full i3 port. But the extra abstraction layer means it can't match the raw speed of Flashspace just making macOS Spaces work properly.

The lesson: when you're trying to reproduce a Linux workflow on Mac, optimize for the feeling first. Get the speed right, then add complexity only if you need it. I needed fast workspaces. I didn't need a tiling tree.

Getting started

Install Flashspace from GitHub or Homebrew
Set up 4 macOS Spaces (Mission Control → add desktops)
In System Settings → Desktop & Dock, disable "Automatically rearrange Spaces based on most recent use"
Configure your keybindings in Flashspace's preferences
Assign apps to workspaces
Disable macOS Space transition animations if Flashspace hasn't already:

defaults write com.apple.dock workspaces-auto-swoosh -bool NO
killall Dock

The whole setup takes ten minutes. The speed difference is immediate.