how to download san francisco font

First, review download instructions here: Human Interface Guidelines.

Next, you can download the current Apple system font (2017) here: San Francisco.

Download is SFPro.zip that contains San Francisco Pro.pkg.

In FontBook, after you run the package you will find SF Pro Display and SF Pro Text.

You can use these fonts to get the exact look and feel for all your app development projects. Not sure about system font conflict, except that Apple Typography has your back. San Francisco does get updated regularly. In my experience, when it updates in a major way, then Apple auto searches any machine containing the download and deletes it, so that it does not conflict. Or sometimes you might want to reinstall OS X depending, whatever. This will be my fourth download since El Capitan, and second download on this Sierra Mac Pro. After my mockup is complete, right click in FontBook and Remove.

If you are not developing, you really don't need this download, because the font is everywhere on your device. It is the default system sans-serif font.... Got to go, designing a mockup APP selection panel for an old friend. Enjoy!

🙂 Apple typography is great!

You don't. It's not that you can't copy the San Francisco fonts of El Capitan to another Mac, but the internal names of every typeface of the San Francisco set is "System font". Which means if you put them on any Mac running any older version of OS X and activate them, they will conflict with the system fonts of those versions of OS X. Don't do it.

To my knowledge, San Francisco cannot be downloaded. It comes standard as the system font in El Capitan.