Kaizu
Free, open-source Mac browser on WebKit: Arc-style spaces, command bar, Arc import and built-in blocking.
Kaizu is a native macOS browser written in Swift on the system WebKit engine, built by Prototype for people leaving Arc. It keeps Arc's sidebar model: spaces with their own pinned tabs, folders and Today tabs that archive themselves, favorites per profile, profiles for separate logins, a command bar, Peek, split view with up to four panes, and little windows for links from other apps. It imports Arc spaces, pinned tabs, folders and favorites from Arc's sidebar file, installs extensions from the Chrome Web Store and Firefox Add-ons, and blocks ads, trackers and cookie pop-ups by default. It has no account or analytics, no sync, no mobile app and no built-in AI. The build is Apple-silicon only, needs macOS 15.4, is signed ad hoc rather than notarized, and cannot use passkeys yet.
79% Arc feature parity (yes = 1, partial = ½).
No AI
No AI features. An opt-in side panel using your own claude.ai/ChatGPT login is only a planned roadmap item, not built.
github.comNot counted in Arc parity: some people want AI, some avoid it.
None found
No account, ads, wallet, feed or upsells. Telemetry is only a roadmap item (opt-in); the updater reads one public version file and sends nothing about you.
github.comAds, crypto, paid upsells, news feeds, default-on telemetry, required accounts.
Organization
| Feature | Kaizu | Arc | Note |
|---|---|---|---|
| Vertical sidebarTabs live in a vertical sidebar that is the main tab UI and can be hidden. | ✓ | ✓ | Vertical sidebar is the only tab UI; Toggle Sidebar (⌘S) hides it and hover peeks it back.github.com |
| SpacesSeveral workspaces per window, each with its own pinned and open tabs, switched by swipe or shortcut. | ✓ | ✓ | Spaces each hold their own pinned and Today tabs; two-finger swipe on the sidebar or the Spaces menu switches.github.com |
| Profiles per Space (shareable)Each Space can use its own browser profile (separate cookies, logins, history), and one profile can be shared by several Spaces. | ✓ | ✓ | New Space asks 'Separate (new profile)' or 'Shared with <profile>'; profiles have own logins and site data.github.com |
| Global favoritesPinned icons at the top of the sidebar shared by every Space (Zen calls them Essentials). | ✓ | ✓ | Favorites belong to the profile, shared by spaces on it; a new space defaults to its own profile.github.com |
| Pinned tabs & foldersPer-space pinned tabs that act like bookmarks, with nested folders. | ✓ | ✓ | Each space has its own pinned section of tabs and nested folders (Arc's tab groups).github.com |
| Auto-archive tabsUnpinned tabs close automatically after a set time and stay recoverable in an archive. | ✓ | ✓ | Today tabs archive after 12 h, 1 d or 7 d (or never); archived tabs are searchable in the command bar.github.com |
| Space themesPer-space colour or gradient themes. | ✓ | ✓ | Each space picks a colour from 8 built-in themes plus Auto/Light/Dark appearance; no custom gradients.github.com |
Browsing
| Feature | Kaizu | Arc | Note |
|---|---|---|---|
| Split ViewTwo or more tabs side by side in one window. | ✓ | ✓ | Up to four tabs side by side; drag a tab onto the page.github.com |
| Link previewOpen a link in an overlay without leaving the current page (Zen calls it Glance). | ✓ | ✓ | Links from favorites and pinned tabs peek in a card; Shift-click peeks any link; card expands to a tab.github.com |
| Mini windowA small, chrome-less window for links opened from other apps or a quick search. | ✓ | ✓ | Links from other apps open in a little window by default; promotable to a tab without reloading.github.com |
| Command barA ⌘T palette that searches tabs, history, bookmarks and browser commands. | ✓ | ✓ | ⌘T bar searches open tabs, history, archived tabs and every menu command, plus unit and currency answers.github.com |
| Link routingRules that send links from other apps to a chosen space or profile. | ✓ | ✓ | Settings → Links: rules by site or path send links from other apps to a chosen space and its logins.github.com |
| Site customizationPer-site custom CSS/JS, or zapping elements off a page. | ◐ | ✓ | Only Hide Distracting Items: click page elements to hide; saved per site as CSS selectors. No custom CSS/JS.github.com |
| Auto picture-in-picturePlaying video pops out into picture-in-picture automatically when you switch tabs. | ✓ | ✓ | Leaving a tab with playing video enters picture-in-picture; on by default, toggle in Settings.github.com |
Compatibility & migration
| Feature | Kaizu | Arc | Note |
|---|---|---|---|
| Arc importImports Arc spaces, pinned tabs and folders. | ✓ | – | File → Import from Arc reads StorableSidebar.json: spaces, pinned tabs, folders, favorites, Today tabs.github.com |
| Chrome extensionsInstalls extensions from the Chrome Web Store. | ✓ | ✓ | Add to Kaizu on Chrome Web Store or Firefox Add-ons pages; runs on WebKit's extension API, not all tested.github.com |
| DRM (Widevine)Netflix, Disney+, Spotify web and other DRM video/audio play. Chromium forks need a Google Widevine licence. | ? | ✓ | |
| PasskeysWebAuthn passkeys, Touch ID and the system/iCloud keychain. | ✕ | ✓ | Bundle is ad-hoc signed with no entitlements; roadmap lists passkeys as blocked pending Apple's entitlement.github.com |
| SyncSpaces, pinned tabs and settings sync across devices. | ✕ | ✓ | No sync; roadmap lists sync across devices as 'later', CloudKit candidate.github.com |
| Mobile appiPhone, iPad or Android app that shares spaces with desktop. | ✕ | ◐ | Mac-only; roadmap lists Windows/iOS apps as not planned.github.com |
Extras
| Feature | Kaizu | Arc | Note |
|---|---|---|---|
| Built-in ad blockerAd and tracker blocking without installing an extension. | ✓ | ✓ | EasyList/EasyPrivacy blocking, YouTube ad removal and cookie-popup rejection, on by default; per-site pause.github.com |
Extension support
Which extension formats and stores run, beyond the Chrome Web Store row above. Not counted in Arc parity.
| Feature | Kaizu | Arc | Note |
|---|---|---|---|
| Manifest V2 extensionsThe older extension format Chrome removed in 2025. Needed for full uBlock Origin and other extensions that block requests. | ◐ | ✕ | WebKit runs MV2 but webRequest can't block, so no full uBlock Origin; Kaizu adds no patch.github.com |
| Manifest V3 extensionsThe current extension format used by the Chrome Web Store (and supported by Firefox and Safari). | ✓ | ✓ | Chrome Web Store MV3 extensions install and run on WebKit's WKWebExtension; not all tested.github.com |
| Firefox add-onsAdd-ons from addons.mozilla.org or .xpi files install and run. | ✓ | ✕ | Add to Kaizu on addons.mozilla.org pages downloads the .xpi; Firefox-only APIs WebKit lacks won't work.github.com |
| Safari extensionsSafari web extensions (the App Store extension apps Safari uses) install and run. | ✓ | ✕ | Settings → Extensions lists Safari web extension apps in /Applications and loads them in place.github.com |