There are exactly 0 fonts built in to browsers. You could try using fonts installed on the system but that tends to devolve in a cross-platform compatibility mess.

There is a set of 7 fonts widely distributed enough to be considered "web safe" if not built in to browsers (and at one point most browsers installed them if they were not already supported by the OS, but today almost all OSes support them directly so most browsers no longer ship them directly), but it's not a particularly great set: Verdana, Trebuchet, Arial, Comic Sans, Georgia, Times New Roman, and Courier New.

Even if those were somehow the 7 "best" fonts in all of the world, there's still a need to support external fonts because fonts are a tool for creative expression. Creative expression might not always be what you want from the web, but as a 90s Web fan, a web without creative expression would be a terrible web.

>need to support external fonts because fonts are a tool for creative expression

Maybe, but using google fonts is as uncreative as you can get.

There's currently 993 font families on Google Fonts from a very wide variety of open license amenable font foundries, in a wide variety of styles (at least for latin scripts). Are you implying it is uncreative to sift through such a large gallery of possible fonts and find ones that speak to you or your project? Or are you implying it uncreative to use open licensed fonts and people should pay for their fonts, perhaps confusing creativity with capitalism? Or are you simply making some sort of stand that to truly create something like an apple pie, first you must create the universe and thus real creatives make all their fonts from scratch one kern at a time?

Google Fonts has problems like privacy concerns definitely, but it seems to facilitate a lot of creativity in web page design that otherwise would seem impossible. (Self-hosting fonts is not fun, and that's assuming you are capable of handling the complex slalom of font licenses, web-capable font licenses, font to webfont conversion tools, etc. There are more options beyond Google Fonts, including for commercial fonts, but Google Fonts is still the most accessible for the wild, free/open source creative parts of the web on low or no budget, the parts most like the 90s web.)

Notably that set of fonts excludes most linux installs, given their licenses.

Fair point, many distros don't bundle by default the fonts because they disagree with the free as in beer but not free as in speech nature of the fonts.

Though many distros still make them available for those that want them. For instance, in Ubuntu they are included in the "Restricted Extras" meta-package, or specifically in the ttf-mscorefonts-installer package.

YC uses font-family:Verdana, Geneva, sans-serif; and it works fine.

Why is that? Why browser makers cannot agree on a set of fonts that are good enough for most, and ship them?

You mean Roboto everywhere? Maybe I have a preference for Lora in the headlines because it goes good with another font in mass text? Fonts are commonly underrated but take a look at some cooperate identities ... you recognize Mercedes every time you see a truck with ads of Mercedes on it because of what? You guessed it right ... fonts. This wouldn't be possible if everyone would use Arial, Verdana and Times New Roman or even Roboto.

If ads are the only use case for fonts, all the more reasons to kill them with fire.

I hate ads as much as everyone else, but branding goes beyond ads and is valuable.

Rasterize your content or serve SVG?

No? There are no fonts built into browsers.