Designed from the ground up for use on all Apple devices, San Francisco has been fine-tuned for optimal readability on a Mac, and looks particularly crisp and refined on a Retina display.
One could argue whether Apple really designed the SF family from the ground up given the almost identical appearance to “Akkurat“, a font designed by the Swiss Laurenz Brunner. Here is a comparison on ExpiredMag:
Back in 2012 on the genesis of Akkurat by Laurenz:
My typeface was an anti-thesis to [graphic design in London in 2002] – a utilitarian typographic notion that, looking back, I was only able to embrace by living a healthy distance from Switzerland, my home country, famed for its modernist heritage.
For a long time I never considered releasing the font – I thought of it as my own personal writing tool. (…) It actually took several weeks for the first license to leave the shop, and it wasn’t until two or three years later that designers started becoming more interested in an ‘objective’ typographic style, reanimating a lot of classic (Swiss) design values. Akkurat became something of a mascot for this movement.
On the other hand Akkurat is very similar to grotesque typeface FF DIN. Apple is know to experiment with humanist typefaces: prior to iOS 9, FF DIN was used in the camera app as the UI font, and another humanist font, Avenir, designed by Swiss Adrian Frutiger, was notoriously used as the font in Apple Maps.
Needless to say, I’m A-okay with the use of SF, and I love the modifications to the original (just check the colon between the time markings), but I’m not so A-okay with the design attribution. Clearly, Antonio Cavedoni, at Apple Type Group, could’ve pushed attributing SF as a font that was based on Akkurat and have been modified as a typeface for Apple’s UI font. Apple in the end has chosen not to.
update: I made some comparison, the difference is more striking here. I think Apple did a good job with the fork, though.