Google has dropped true screen mirroring on us at I/O 2014. It's been a long time coming, but Chromecast is finally getting mirroring of photos, videos, live apps and even views from your camera viewfinder, right on your TV with Chromecast. Anything that is on your screen, you'll be able to throw it to your Chromecast soon. Screen mirroring is going to be supported on the Nexus 4 and then support for other devices will come later. Those devices will include the HTC One M7, LG G2, Samsung Galaxy S4, S5, and Note 3, with others coming in the future.
One of the coolest new things with Chromecast is the ability to share access the dongle and change content without needing to be on the same Wi-Fi network. Google is making this happen using a combination of techniques including location data to determine whether or not users are in the same place as a Chromecast device. This means you just have to be in the same room as your Chromecast to access it. It also means you don't have to give out your Wi-Fi password to your friends so they can access your Chromecast. You can't troll your friends by using their Chromecast from your own house, unfortunately.
There's more new stuff besides Google Cast coming to Chromecast. There's a new website that makes it easier than ever to find apps for their Chromecast. You can go to chromecast.com/apps and see everything that's available for your device.
There's also something called Backdrop that steps up the standard photo screensaver on Chromecast, too. It will let you display photos, weather info, news, and famous artwork on your TV while you're not actively using your Chromecast. You set up Backdrop through an Android or even an iOS device and choose what you want it to display. Backdrop integrates with Google Now, letting you ask your phone "What's on my Chromecast?" to get more information about whatever Backdrop is displaying on your TV.