Apple File System (APFS) to replace HFS Plus, will work on all Apple devices
APFS didn't get any spotlight at this year's WWDC, but is nonetheless an important step toward a unified experience across wearables, mobile and desktop devices. Apple isn't all that keen on sharing a lot of details about APFS right now, but its developer portal offers some info for the curious:
APFS developer preview is available with macOS Sierra 10.12, with a final build aimed at a 2017 release. In its current state, the file system is still quite rough around the edges – which is to be expected from an early preview – in that it can't be used as a startup disk and doesn't run on Apple's proprietary hybrid Fusion Drives.
As for improvements over the current HFS Plus, Apple promises:
Beyond the aforementioned Flash/SSD storage optimizations, APFS is expected to add copy-on-write metadata, space sharing, cloning of files and directories, snapshots and fast directory sizing, among other features. APFS is scheduled for an official release in 2017.
source: Apple via Redmond Pie