By way of apology for my modest rant about “Is it done yet?” regarding HTML5 on my Google+ account, I offer the following list of resources for testing, readiness and support for various browsers and platforms.
Find Me By IP
Along with many other tools, Find Me By IP offers an easy to read and fairly robust chart of HTML5 support by browser. The same page also lists CSS3 support reference which is quite handy since HTML5 and CSS3 often go hand in hand in many people’s minds.
Microsoft Internet Explorer Test Center
A bit harder on the eyes than Find Me By IP, the MS IE Test Center is even more robust. However, being a MS resource you might notice that the focus can lean a tad towards what IE9+ supports over other browsers, than what it does not. Used in conjunction with other site, though, it has some useful data.
When Can I Use…
I spent several minutes here, checking and unchecking boxes and running various searches and comparisons. Looks like it would be very useful for doing detailed research on your particular project’s user base before deciding on whether or not a particular feature was a good solution for you.
Upon visiting this site, it will immediately test the browser you are using at the moment and assign it a score based on its support for HTML5 (and some “bonus features”). This can take a minute or three so don’t worry if you don’t immediately see anything, Once the test is complete, you can also toggle over to “Other Browsers” to see how your current browser stacks up.