They use Swift Playgrounds to do a lot of development:
"Swift Playgrounds for iterative development and styling. Most major screens in the app get a corresponding playground where we can see a wide variety of devices, languages, and data in real time."
"Swift Playgrounds for iterative development and styling. Most major screens in the app get a corresponding playground where we can see a wide variety of devices, languages, and data in real time."
https://github.com/kickstarter/ios-oss/tree/master/Kickstart...
I've recently bought into this development method too. It's not quite what Bret Victor dreamed up, but it's a big step in the right direction.