Circa
Free, open-source native Mac browser (Swift/AppKit, Chromium) with Spaces, Peek, Little Circa and Boosts.
Circa is a free, MIT-licensed Mac browser with a Swift and AppKit interface on a patched Chromium 156 (CEF) engine. It pitches itself at Arc users: a sidebar, Spaces tied to profiles, pinned tabs and folders, auto-archive, a Command Bar, up to four-way Split View, Peek, Little Circa, per-site CSS/JavaScript Boosts, Air Traffic Control-style link rules and an Arc importer. Chrome Web Store extensions work, iCloud sync is optional, and AI (Codex, Claude Code or Apple on-device) is off by default. Builds are signed, notarized and auto-update, but it is Apple Silicon and macOS 15+ only, and a README labels it preview software. Favorites are per profile, and I found no built-in ad blocker. Widevine DRM and passkeys were not verified.
79% Arc feature parity (yes = 1, partial = ½).
AI optional
Off until you turn AI on in Settings and pick Codex, Claude Code or Apple's on-device model; then page chat, summaries, tab tidying, Skills, Boosts, Errands.
github.comNot counted in Arc parity: some people want AI, some avoid it.
None found
No ads, wallet, feed, upsell or account (README: no browser account needed). Sparkle update checks send no system profile; no analytics SDK found in the source.
github.comAds, crypto, paid upsells, news feeds, default-on telemetry, required accounts.
Organization
| Feature | Circa | Arc | Note |
|---|---|---|---|
| Vertical sidebarTabs live in a vertical sidebar that is the main tab UI and can be hidden. | ✓ | ✓ | Tabs live in a sidebar; View > Show/Hide Sidebar (Cmd+S) hides it.github.com |
| SpacesSeveral workspaces per window, each with its own pinned and open tabs, switched by swipe or shortcut. | ✓ | ✓ | Spaces menu with Next/Previous (Opt+Cmd+arrows) and Ctrl+1-9; each Space has its own pinned tabs.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. | ✓ | ✓ | Each Space has a profile; Change Profile moves it to an existing or new one, so Spaces can share.github.com |
| Global favoritesPinned icons at the top of the sidebar shared by every Space (Zen calls them Essentials). | ◐ | ✓ | Favorites are stored per profile; Spaces on different profiles show different Favorites.github.com |
| Pinned tabs & foldersPer-space pinned tabs that act like bookmarks, with nested folders. | ✓ | ✓ | Pinned tabs are kept per Space and hold nested folders; New Folder is in the Tabs menu.github.com |
| Auto-archive tabsUnpinned tabs close automatically after a set time and stay recoverable in an archive. | ✓ | ✓ | Today tabs auto-archive after a set delay (up to 30 days) and stay in an Archived Tabs view.github.com |
| Space themesPer-space colour or gradient themes. | ✓ | ✓ | Each Space carries its own gradient theme with light and dark variants.github.com |
Browsing
| Feature | Circa | Arc | Note |
|---|---|---|---|
| Split ViewTwo or more tabs side by side in one window. | ✓ | ✓ | Up to four panes side by side (Ctrl+Shift+= adds a split).github.com |
| Link previewOpen a link in an overlay without leaving the current page (Zen calls it Glance). | ✓ | ✓ | Shift-click, or a link leaving a pinned tab's site, opens a Peek overlay; both on by default.github.com |
| Mini windowA small, chrome-less window for links opened from other apps or a quick search. | ✓ | ✓ | Little Circa window is the default destination for links opened from other apps.github.com |
| Command barA ⌘T palette that searches tabs, history, bookmarks and browser commands. | ✓ | ✓ | Cmd+T/Cmd+L palette searches open tabs, pinned tabs, history, archived tabs and actions.github.com |
| Link routingRules that send links from other apps to a chosen space or profile. | ✓ | ✓ | Ordered rules (URL contains, equals or host) send external links to a chosen Space.github.com |
| Site customizationPer-site custom CSS/JS, or zapping elements off a page. | ✓ | ✓ | Per-host Boosts with custom CSS, custom JavaScript and zapped elements.github.com |
| Auto picture-in-picturePlaying video pops out into picture-in-picture automatically when you switch tabs. | ✓ | ✓ | Playing video enters picture-in-picture when you leave the tab; on by default, per-site toggle.github.com |
Compatibility & migration
| Feature | Circa | Arc | Note |
|---|---|---|---|
| Arc importImports Arc spaces, pinned tabs and folders. | ✓ | – | Imports Arc Spaces and tabs (passwords where available), including archived and Today tabs.github.com |
| Chrome extensionsInstalls extensions from the Chrome Web Store. | ✓ | ✓ | Installs from the Chrome Web Store on Chromium 156; README says compatibility is still evolving.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. | ? | ✓ | |
| SyncSpaces, pinned tabs and settings sync across devices. | ✓ | ✓ | Optional iCloud sync of Spaces and tab organization; no Circa account needed.github.com |
| Mobile appiPhone, iPad or Android app that shares spaces with desktop. | ✕ | ◐ | No mobile app; the mobile folder only says one is planned for the future.github.com |
Extras
| Feature | Circa | Arc | Note |
|---|---|---|---|
| Built-in ad blockerAd and tracker blocking without installing an extension. | ✕ | ✓ | No ad or tracker blocker in the feature list or source; extensions are the route.github.com |
Extension support
Which extension formats and stores run, beyond the Chrome Web Store row above. Not counted in Arc parity.
| Feature | Circa | Arc | Note |
|---|---|---|---|
| Manifest V2 extensionsThe older extension format Chrome removed in 2025. Needed for full uBlock Origin and other extensions that block requests. | ? | ✕ | |
| Manifest V3 extensionsThe current extension format used by the Chrome Web Store (and supported by Firefox and Safari). | ✓ | ✓ | Chromium 156 extension host with Web Store install; MV3 DNR support not tested.github.com |
| Firefox add-onsAdd-ons from addons.mozilla.org or .xpi files install and run. | ✕ | ✕ | Chromium extensions only; README says Firefox extensions are not imported.github.com |
| Safari extensionsSafari web extensions (the App Store extension apps Safari uses) install and run. | ✕ | ✕ | Chromium extensions only; README says Safari extensions are not imported.github.com |