San Francisco is a sans-serif typeface family designed by Apple. It was first created for use on the Apple Watch and has since gone on to replace Helvetica Neue as the system font on OS X and iOS. I imagine it will likely replace Myriad as Apple’s official advertising typeface in the near future. San Francisco is available in two distinct versions: SF, which is used on iOS and OS X and SF Compact, which is used on the Apple Watch. SF Compact features letterforms with flatter sides which allows spacing to be set more tightly. Both versions are available in two optical sizes, Text and Display, although I question the usefulness of a display version on such a tiny watch screen. I’ve heard San Francisco accused of being a knockoff of Lineto’s Akkurat but it is actually quite different—San Francisco features a single-story g and lacks a tail on the l.
Font research done for you.