1. HTML5 Test http://html5test.com/
The HTML5 Test website will allow you to see how well a specific version or brand of browser implements the whole of the HTML5 specification. This is very useful when you are trying to decide what kind of browser or device support matrix your application will provide.
2. Can I Use http://caniuse.com/
The Can I Use website goes into more detail and allows you to look at a specific HTML element or attribute and see which browser vendors have implemented it and in which versions of their browsers.