Button creates deep links between mobile apps so that tapping a button in one app performs that function in another.
Imagine this scenario. You want to get a reservation for four at your favorite restaurant. How do you do it? Chances are, even if you're on a smartphone, you open your web browser, Google the restaurant's URL, and click the "Make a reservation" link. You probably don't open an app like OpenTable or Resy first, even though the experience is better, because you just don't know which app or service your restaurant is partnered with . . . if any!
The makers of Button think they've found a solution, by allowing apps to pass users back and forth between each other to perform actions, kind of like a cross between UI and ads. The idea is to provide broader access to information within the streamlined experience of an app.
Button works by making it easy for developers to drop code-integrating contextual buttons into web pages and apps. Those buttons perform discrete actions in other web pages and apps. In the aforementioned scenario, a visit to my favorite restaurant's website might contain a Button, allowing me to specify the time and date I want a reservation, then continue to the reservation process in the OpenTable app on my phone. Or maybe my music app would have a Button, so when I'm listening to my favorite album I can open up the Ticketmaster app to buy live tickets for the band's next show.
What if the right app isn't installed on my smartphone? In that case, a Button would launch that app's App Store page, while storing its context. For example, if a Foursquare user doesn't have OpenTable, the user could tap the OpenTable Button, select a time for his or her party size on the Commerce Card, and be taken to the App Store. Once the app is finished downloading, the user then would be brought to that specific reservation in OpenTable, with all of their previously filled-in details intact.
That's why Buttons are also a good solution to the problem of discoverability. When every app is a silo unto itself, users are always left second-guessing whether the app they've opened is the one they actually need. Buttons not only allow for apps to more elegantly hand users over to the right app, but to raise awareness of their apps contextually. In a sense, Buttons are almost like interactive ads, except users want to tap on them, because they're also UI elements.
Buttons aren't conceptual. Foursquare, among others, features Buttons from Uber, OpenTable, Ticketmaster, Delivery.com, and Groupon. If you're a developer or a publisher, you can add Buttons from OpenTable, TicketMaster, Uber, and more to your website or app here.