A list of all the new toys to play with as a web developer in iOS 9 Safari. 3D Touch, new Responsive Web Design breakpoints, native integration and HTML5 APIs; there’s a lot to get your hands on.
Chris Coyier outlines a server-side approach to cutting the mustard (the technique employed in the BBC News website to serve users relevant content based on their device capability).
Shame on you mobile Safari on iOS! Great breakdown on mobile browser cache sizes.
Then http://browserhacks.com is the site for you!
Some good stuff on this article on 20 Snippets You should be using from Html5 Boilerplate.
Lots and lots and lots on responsive web design here.