Want to start rocking HTML5 and CSS3? Of-course you do; but I am sure you don’t want to spend hours and hours researching which tags you can safely use without braking your site for anyone not on a bleeding edge browser. Fear not howecer as http://html5please.us/ has you coverd.
http://html5please.us is a fantastic resource that not only covers what aspects of HTML5 and CSS3 you can use safely, but also lets you know what fallbacks and polyfills are available to help get that much needed support in older browsers.
HTML5 Please is a community project (contribute on github!) from the people behind HTML5 Boilerplate, Modernizr & CSS3 Please. Divya Manian , Paul Irish, Tim Branyen, Connor Montgomery, Jake Verbaten and more!