After going Open Source, the React Native Playground keeps getting better.
The guys behind this awesome tool just announced the

React Native Playground iOS app

Run, test and share React Native applications directly on an iOS device Build an app in the browser on http://rnplay.org and share it with anyone! Explore the site via popular apps, staff packs or search.

What this does mean is that you can write React Native apps in the browser on

React Native Playground

generate the QR Code and then run, test and share them on real iOS devices.