YabSigmaOS vs Zen
SigmaOS is a Mac browser on WebKit that treats tabs like a to-do list, in workspaces down the side, with an AI assistant called Airis.
Zen is a free, open-source browser built on Firefox that brings Arc’s layout, tabs down the side with spaces, folders and Split View, to Mac, Windows and Linux.
The short answer
- if you want workspaces and tabs you mark done, on a Mac
- if you browse by keyboard, with single-key shortcuts
- if you prefer WebKit to Chromium and want spaces
- if you want Arc’s layout, free and open source
- if you prefer Firefox’s engine and its add-ons
- if you want no AI in your browser at all
- if you miss Arc and want spaces, pins and folders kept, on a Mac
- if you already pay for Claude or ChatGPT and want it to work in your signed-in tabs
At a glance
SigmaOS and Zen, with Yab beside them for a Mac.
| What | SigmaOS | Zen Browser | Yab |
|---|---|---|---|
| Made by | SigmaOS Inc. (London) | Zen Browser team (open-source community project) | Serafim Korablev |
| Status | No release notes since February 2025 | Updated | Updated |
| Runs on | Mac | Mac, Windows and Linux | Mac |
| Phone app | None; Mac only. iOS has been on its roadmap since 2021 | None; Zen says it has no plans for a mobile version | Not yet |
| Price | Free; Personal Pro $20/month or Personal Max $30/month for more AI | Free and open source | Free; its AI runs on your own Claude or ChatGPT plan |
| AI | Chat about pages, on its own AI service | No AI | An agent that works in pages, on your Claude or ChatGPT plan |
| Driven by outside agents | No | No | MCP and a command line |
| Engine | WebKit | Gecko | WebKit |
| Tabs down the side | Yes | Yes | Yes |
| Spaces | Yes | Yes | Yes |
| Split View | Yes | Yes | Yes |
| Extensions | Chrome Web Store | Firefox add-ons | Chrome Web Store |
| Ad blocker | Built in | No | Built in |
| Open source | No | Yes | No |
Checked October 9, 2026 on each maker’s own pages, linked under Sources. Prices are per month, in US dollars.
Where they differ
What separates them, area by area. Where one plainly has more, it says who; where it comes down to taste, it says so.
AISigmaOS leads
SigmaOS has AI built in; Zen has less of it. Airis chats about the page you are on, sums it up, looks things up and translates; no agent. Zen has no AI: Firefox’s AI features are switched off by default.
Tabs and windowsZen leads
SigmaOS has tabs down the side, spaces and Split View. Zen has tabs down the side, spaces, Split View, folders in the sidebar and tabs that sleep.
PriceSigmaOS leads
SigmaOS: Free; Personal Pro $20/month or Personal Max $30/month for more AI. Zen: Free and open source.
Where it runsZen leads
SigmaOS runs on Mac. Zen runs on Mac, Windows and Linux. On a Mac, SigmaOS needs macOS 12 or later and Zen needs macOS 10.15 or later. SigmaOS has no phone app: Mac only. iOS has been on its roadmap since 2021. Zen has no phone app: Zen says it has no plans for a mobile version.
Engine and extensionsa matter of taste
SigmaOS is built on WebKit, the engine Safari uses; Zen on Gecko, Firefox’s engine. SigmaOS takes extensions from the Chrome Web Store, Zen from Firefox’s add-ons.
Privacyeven
SigmaOS has an ad blocker built in. SigmaOS keeps history and cookies on your Mac unless you turn on sync, stored encrypted on AWS; its privacy policy doesn’t say where Airis requests go. Zen has open code. Zen sends no telemetry or crash reports, by its privacy policy; optional sync keeps encrypted data on Mozilla’s servers.
UpdatesZen leads
SigmaOS: Still downloadable, with no public release notes since version 1.19 in February 2025. Zen is updated as usual.
What their pages don’t lead with
Real limits, from the makers’ own words and our own use.
SigmaOS
- Mac only
- No public release notes since version 1.19 in February 2025
- Chrome extensions only partly work, behind its WebKit+ option
- Its AI is an assistant, and regular use needs the $20 or $30 plans
Zen Browser
- Releases are still labeled beta
- No phone app, and none planned
- Firefox add-ons only, not the Chrome Web Store
- No ad blocker of its own beyond Firefox’s tracking protection
Yab, honestly
- Mac only: macOS 15.4 or later, no Windows, iPhone or Android
- New: first released in September 2026
- Its AI needs a Claude or ChatGPT plan; ChatGPT’s free plan may work with low limits
- WebKit, as in Safari: a site tested only in Chrome can misbehave
- Closed source
What changed lately
- September 5, 2026Zen: Spaces, folders and tabs sync between devices with a Mozilla account (1.22b)
- February 28, 2026Zen: Live folders for GitHub issues, pull requests and RSS (1.19b)
- August 27, 2025Zen: Tab folders added (1.15b)
- February 4, 2025SigmaOS: Version 1.19.0, a performance update, the last release with public notes
Questions
Is SigmaOS free?
Yes, with limits on its AI. Free; Personal Pro $20/month or Personal Max $30/month for more AI.
Is Zen Browser free?
Yes. Free and open source.
Which has an AI agent, SigmaOS or Zen?
Neither has an agent that does tasks in your pages. Airis chats about the page you are on, sums it up, looks things up and translates; no agent. Zen has no AI: Firefox’s AI features are switched off by default.
Which runs on Windows, SigmaOS or Zen?
Zen does. SigmaOS runs on Mac.
Do SigmaOS and Zen have phone apps?
SigmaOS has no phone app: Mac only. iOS has been on its roadmap since 2021. Zen has no phone app: Zen says it has no plans for a mobile version.
Is SigmaOS still being updated?
Still downloadable, with no public release notes since version 1.19 in February 2025.
Is there a third option on a Mac?
Yab, Yet Another Browser, is free for the Mac: tabs down the side with spaces, folders and Split View, as in SigmaOS; an agent that works in your signed-in tabs, on the Claude or ChatGPT plan you already pay for. Claude Code, Codex and any MCP client can drive it too. It runs on WebKit, the engine Safari uses, and takes Chrome extensions. It is Mac only, and new.
More comparisons
- SigmaOS home page
- SigmaOS upgrade (plans)
- SigmaOS download (macOS only)
- SigmaOS update feed (appcast)
- SigmaOS 1.19.0 update notes
- SigmaOS 1.17.0 update notes (password manager)
- SigmaOS common questions
- SigmaOS docs: ad blockers and WebKit+
- SigmaOS docs: migrating from Arc
- SigmaOS privacy policy
- TechCrunch: SigmaOS turns to AI features for monetization (2024-03-26)
- Launch HN (Aug 16, 2021): founder says iOS and iPadOS are on the roadmap
- Zen home page
- Zen download page (macOS universal, Windows, Linux; beta)
- Zen 1.23.2b release (macOS universal dmg; Info.plist minimum 10.15)
- Zen 1.23.1b release (Firefox 157.0.1)
- Zen license (MPL-2.0)
- Zen AI preferences (all off)
- Zen welcome flow (Firefox import wizard)
- Firefox import from another browser
- Zen 1.15b release (folders)
- Zen 1.19b release (live folders)
- Zen 1.22b release (sync)
- Zen 1.12.9b release (tab unloader uses Firefox tab discarding)
- Zen FAQ (no mobile plans, donations)
- Zen Workspaces
- Zen Split View
- Zen Extensions (addons.mozilla.org)
- Zen Privacy and Security (Firefox password manager, tracking protection)
- Zen privacy policy
- Firefox 157 system requirements
- Yab Manual: Bringing in from another browser
- Yab Manual: Connecting Claude or ChatGPT
- Yab Manual: Extensions
- Yab Manual: Yab’s tools over MCP
- Yab Manual: Privacy
Yab, Yet Another Browser.
Free for the Mac. Arc’s sidebar, your own Claude or ChatGPT as the agent, Chrome extensions on WebKit.