Files and Directory Entries API
The Files and Directory Entries API allows browsers to find, create, and edit files in a sandboxed environment. It remains to be seen what Apple does with this, and it’s not yet a full web standard.
Elliptic Curve P-521
Elliptic Curve P-521 Is an approach to encryption designed to offer the the same levels of encryption as other schemes, but with shorter (smaller) encryption keys.
Safari Technology Preview 41
There are 38 more features and bug fixes in the release, too, including changes to: CSS, WebRTC, Drag and Drop, Web API, JavaScript, WebGL, Media, Rendering, Accessibility, Storage, Web Driver, and Web Inspector.
Developers (or others wanting to living on the browser bleeding edge) can download Safari TP41 from the WebKit.org website.