The Apple TV app is something you can already have if you're an iPhone or iPad user, but Apple intends its TV service to extend far beyond its own hardware.
To that end, Apple is putting the Apple TV app on Samsung smart TVs starting this spring, and it's scheduled to arrive on Amazon's Fire TV, LG TVs, Roku-powered TVs, Sony TVs, and Vizio TVs "in the future."
That's a major move for Apple, and an open concession to the much larger world of TV owners who don't have Apple's set-top box, the Apple TV.
Of course, if you're an iPhone, iPad, or Apple TV owner, you'll simply receive an update this May that will add Apple TV Channels. TV Plus isn't expected to arrive until some point in the fall, also as part of the Apple TV app.
Another first: Apple is bringing its Apple TV app to Macs in the fall. There doesn't appear to be a way to access Apple TV Plus or Apple TV Channels from a web browser.