The real "feature" of the Chromecast isn't technical. It's the ecosystem and particularly the fact it "just works" and is built in and enabled by default on a large number of Android apps. So for example, my friend can come over to my house and fire up his Google Music and his phone automatically sees my Chromecast and he can play to it. Or movies, or photos or ... etc etc. You can get any number of devices that do this, but only the Chromecast is built in and enabled by default on every Android device (not sure what iOS status is ...).