[unicornporn]

I really must recommend Inter[1]. It's also open-source and available as variable.

[1] https://rsms.me/inter/

[flixic]

Inter is almost as good as Apple's SF, and with a much more permissive license. It's my default when designing apps for the web.

I used to default to "system font stack", but that was always because SF is such a great font. Defaulting to Ubuntu font on Ubuntu is... unfortunate. Luckily, Inter is fantastic, and it can be fantastic on every OS.