Much like other modern filesystems such as ZFS and BTRFS it supports shared storage spaces, snapshots, copy-on-write and also has encryption built-in as a first class feature including multiple keys and per-file keys.

More information: https://developer.apple.com/library/prerelease/content/documentation/FileManagement/Conceptual/APFS_Guide/Introduction/Introduction.html#//apple_ref/doc/uid/TP40016999-CH1-DontLinkElementID_27

Today's developer beta ships with support but with many limitations, so it's clearly still a work in progress.

Surprising note buried in the documentation: "An open source implementation is not available at this time. Apple plans to document and publish the APFS volume format when Apple File System is released in 2017."