Unlike most browsers out there, SigmaOS does not contain a single line of Google code. Based on Apple's WebKit engine—the same one that powers Safari—it is well integrated with macOS (it is not available on other platforms, and probably never will be), and feels like a continuation of the operating system. Its performance is good, but pretty average for a web browser, using more energy and memory on idle than Vivaldi, but less than Arc. The interface is very similar to that of Arc: vertical tabs on the left, organized into workspaces which can be accessed by a column of icons on the far left of the window. The address bar is at the top, with all of the usual buttons, as well as some unique features. Pressing 'S' or clicking an icon in the address bar will generate an AI summary of the current webpage, while pressing 'A' will open an AI assistant called Airis, based on OpenAI's GPT-3.5. Airis can use the open tab to inform its responses, though it cannot access the wider internet. A second tab can also be opened as a split screen in this right panel by dragging it to the bottom of the tab stack. Despite being a WebKit-based browser, SigmaOS supports Chrome extensions, which are displayed in this right panel when opened. 

When opening a new tab, you get a menu very similar to Arc's, which gives search suggestions as well as open tabs and commands. Pressing Command + enter after a search opens a mode called "Look it up", similar to Arc Sarch's "Browse for Me", which reads a bunch of websites and generates a summary. You can also ask follow-up questions which will make it generate more content, kind of like ChatGPT. Unlike Airis, this mode can do internet research, though it is quite slow.

One very useful feature is the ability to integrate a password manager of your choice with the browser to replace the default iCloud-based autofill. During the onboarding process, a screen appears with a list of password managers. Choosing an option other than the SigmaOS keychain will cause SigmaOS to intall its extension and allow you to connect your account. The password manager then becomes the default autofill and passwords saved from the browser go there rather than to the built-in keychain. You can also connect a password manager later from the settings window.

Another unique feature which sets SigmaOS apart is the ability to share workspaces with other people. This adds a new "Shared" section of tabs that all collaborators can see, while each parson also has private tabs in the space. You can invite other SigmaOS users with a link and also set whether they can edit the shared pages.

SigmaOS has a pretty steep learning curve. There are so many shortcuts, many of which are triggered by only letter keys and therefore don't work while typing. The browser gave me a popup at one point telling me to hold the function key in order to use shortcuts, which resolves the issue but is mentioned nowhere else. Whenever you click on a feature for the first time, which happens a lot since there are so many features, a popup appears explaining how to use it, which helps reduce the learning curve, but the browser is definitely not intended for casual users. 

In terms of privacy, SigmaOS is pretty good. It comes with its own tracker blocker and the option to add uBlock Origin, which I reccomend pairing with other extensions such as Privacy Badger to get full protection. Its Panopticlick results were the same as Arc and it performed well in all aspects except fingerprinting (it isn't a common browser, so that is to be exprected). Their privacy policy is good, though it does mention analytics, and as a UK-based company they are subject to GDPR. However, if privacy is your top priority, SigmaOS may not be for you.

If you are a power user looking for a sleek, organized browser and are fine sacrificing a bit of privacy (not to SigmaOS itself, just that it won't protect you as well as something like Brave), I would definitely reccomend this browser to you. However, if you just use a few websites and want a simple browser that will work right away, SigmaOS is not that browser. Its high learning curve renders it a niche product, but in that niche it excels.