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.
Built-in AI
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.comBloat check
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 |
|---|---|---|---|
| SidebarVertical 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 |
| ProfilesProfiles 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 |
| FavoritesGlobal 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 TabsPinned 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 |
| Live foldersSidebar folders that fill and refresh themselves from an outside source, such as GitHub pull requests or an RSS feed. | ✕ | ✓ | Arc import skips live folders as a service Kaizu does not talk to; folders are manual only.github.com |
| ArchiveAuto-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 |
| Theme pickerSpace 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 |
| PeekLink 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 |
| Little ArcMini 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 |
| Air Traffic ControlLink 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 |
| BoostsSite 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 PiPAuto 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 |
| Mini playerMedia still playing in a tab you left keeps play/pause controls in the sidebar. | ✓ | ✓ | Sidebar card for media playing in a tab you left: pause button and click to return; no skip or mute.github.com |
| Tab SwitcherRecent-tab switcherCtrl+Tab jumps back to the tab you used last and cycles in recently used order. | ✓ | ✓ | ⌃Tab opens a thumbnail switcher of the space's tabs in most-recently-used order; releasing ⌃ switches.github.com |
| Super CopyClean link copyA shortcut (⌘⇧C) copies the page URL with tracking parameters removed. | ✓ | ✓ | ⇧⌘C Copy Link strips tracking parameters and shows a "Copied link" confirmation; ⌥⇧⌘C copies as Markdown.github.com |
| CaptureScreenshotsBuilt-in capture of a chosen area or element, and of the full page. | ◐ | ✓ | ⇧⌘2 drags an area or copies the visible page; whole page only via Export as PDF, not an image capture.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 streamingNetflix, Disney+, Spotify web and other DRM video/audio play, through Widevine or, on WebKit, FairPlay. Chromium forks need a Google Widevine licence; FairPlay counts once a major service is confirmed playing in the app. | ? | ✓ | |
| 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 |
| Custom ShortcutsShortcut editorMost browser keyboard shortcuts can be remapped in Settings. | ◐ | ✓ | Help lists shortcuts read-only; Settings only lets you pick the global quick-search hotkey from three combos.github.com |
More Arc features
Arc features shown but not counted in the score, because almost no replacement has them or only a few people need them.
| Feature | Kaizu | Arc | Note |
|---|---|---|---|
| EaselsA shareable canvas of live page captures, notes and drawings. | ✕ | ◐ | Roadmap lists Easels as not planned; Arc import skips them.github.com |
| Shared CollectionsShared spaces & foldersShare a Space, folder or set of tabs as a link anyone can open, or another user can add to their sidebar. | ✕ | ✓ | Roadmap lists only a page-level Share in the right-click menu; no space, folder or tab-set sharing.github.com |
| PreviewsWeb app previewsHover a pinned Gmail, Calendar or other web app to glance at it; a pinned calendar shows the next meeting with Join. | ◐ | ✓ | Favorite tiles show a dot when a site notification arrives; no live content glance or next-meeting widget.github.com |
| Developer modeA developer view that turns on by itself for localhost: full URL, quick DevTools and dev tools in reach. | ✕ | ✓ | Roadmap says Kaizu is "not a developer tool"; pages are only inspectable, with no dev mode.github.com |
Extension support
Which extension formats and stores run, beyond the Chrome Web Store row above.
| 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 |