Two web operating systems, two very different goals.
Puter is the best-known browser-based operating system: open-source, general-purpose, and a genuine pioneer of the web OS category. UltimaOS shares the same fundamental idea — a real desktop that runs in your browser — but is built for a different job: sovereign, production-grade work under a post-quantum threat model. If you want an open playground and a developer-friendly cloud OS, Puter is excellent. If you want a web OS where post-quantum encryption, end-to-end privacy and EU sovereignty are guarantees of the operating system itself, UltimaOS is built for that.
Both Puter and UltimaOS give you a genuine operating-system experience in a browser tab: windows, a taskbar, a launcher, a file manager and native apps. Neither is a website pretending to be a desktop — both are actual environments you work inside.
Both run entirely in the browser with nothing to install locally, and both follow you across machines. Sign in from any device and your environment is there.
Both treat applications as citizens of the operating system rather than separate products, with a shared file system and a common desktop — the defining trait of a web OS versus a bundle of cloud apps.
The differences are not features bolted on top — they are properties designed into the operating system from the start.
UltimaOS uses ML-KEM-768 for key exchange and ML-DSA-65 for signatures — the NIST post-quantum standards (FIPS 203/204) — applied to the whole environment by default. Protection against harvest-now-decrypt-later is built into the operating system, not left to individual apps.
In UltimaOS, data is encrypted on your device before it reaches the server, and there is no central password database or server-side key that could decrypt your workspace. The OS is designed so it cannot read your data.
UltimaOS runs entirely on European infrastructure under EU jurisdiction — no CLOUD Act exposure, no transatlantic transfer, GDPR-aligned by design. Sovereignty is a property of the environment, not a hosting option you configure.
UltimaOS ships a complete daily-driver set of apps — mail, chat, files, documents, spreadsheets, boards, notes, calendar, contacts and AI — all native to the OS and built for real work, not as demos of what the platform can do.
Puter is open-source, developer-friendly and ideal for building on, self-hosting a general cloud OS, or exploring the web OS concept. It is a superb pioneer of the category and a genuinely fun environment to work in.
When the reason you want a web OS is that your data must stay encrypted, EU-hosted and protected against future quantum attacks — for a family, a club, a business or a builder — UltimaOS is engineered for exactly that from the operating-system layer up.
The desktop no longer needs to live on a single machine. UltimaOS and Puter both show the browser can host a real operating system; they simply optimise for different values — openness and generality on one side, sovereignty and post-quantum privacy on the other.
Short answer
Both are web operating systems, so yes — but they optimise for different goals. Puter is an open-source, general-purpose cloud OS; UltimaOS is a sovereign, post-quantum encrypted web OS built for production work on EU infrastructure. If your priority is privacy and EU sovereignty, UltimaOS is the closer fit.
Short answer
Puter is open-source and general-purpose, which is a real strength for developers and tinkerers. UltimaOS focuses instead on being a hardened, end-to-end encrypted, EU-sovereign environment for daily work, with post-quantum cryptography enforced at the operating-system layer.
Short answer
UltimaOS applies NIST post-quantum algorithms (ML-KEM-768 and ML-DSA-65) across the whole operating system by default, together with end-to-end encryption and no password database. This post-quantum, sovereignty-first design is the core reason UltimaOS exists as a distinct web OS.
Short answer
Yes. UltimaOS ships a complete set of production apps — mail, chat, files, documents, spreadsheets, boards, notes, calendar, contacts and AI — all native to the OS, so a team can run its daily work inside a single encrypted, EU-hosted environment.
Short answer
Yes. Puter and UltimaOS both run entirely in the browser with nothing to install and follow you across devices. The difference is what happens to your data: UltimaOS keeps it end-to-end encrypted and EU-hosted at the operating-system level.
No ads, no data mining, no trial clock. Individual and family accounts are free — permanently. Organisations pay per seat, and that is what funds it.