The image above is actually a mock-up created by 9to5mac after they saw a phone running the new OS; the source of the leak wouldn't provide real screenshots in case he got in trouble. The main take-home, though: it's flat. Very, very flat.
9to5mac explains that app icons have been totally redesigned across the board. Interestingly, there seem to be two sets of icons, too: one black-ish and one white-ish. There's also a pair of keyboard color schemes—black with gray letters or gray with white letters.
It's not clear if the pair of color schemes is a decoy, whether it's to tie in with black and white iPhones, or if it's some clever design trick for different lighting situations. But it will be interesting to find out later if that's actually a thing or not.
Elsewhere, the iOS seems to be using a font like Helvetica Nueue Ultra Light—or something extremely similar. Also, up top, the carrier signal bars have been replaced by 5 dots that are white or gray depending on signal strength, which looks nice and neat.
In terms of functionality, 9to5mac has heard from sources that Maps will now feature walking directions, and that Airdrop will be integrated into a sideways scrollable row on top of the device.
Of course, whether any of this will actually turn out to be true is up for discussion. But one thing is certain: we don't have long to wait before we find out. [9to5mac]