The Google Cast Receiver while it’s not an app you would open and navigate it’s one that makes an appearance in every Android TV users life quite often. It’s the bread and butter of how casting is so smooth and “just works”.
If you want to be on the cutting edge of casting then Google just opened the program for you, a beta program. Sign up here for it.
Just a few notes if you want to leave the beta you’ll have to wait up to a few weeks since that’s how often firmware is released.