Expo
Expo is the easiest way to start building a new React Native application. It allows you to start a project without installing or configuring any tools to build native code - no Xcode or AndroidStudio installation required (with some mild disclaimers).
$ npm install -g expo-cli
$ expo init AwesomeProject
$ cd AwesomeProject
$ npm start
Running 'npm start' runs the 'expo start' script set in the package.json file . This runs a command line interface (cli) which gives you options on how to run the app ('i' for iOS, 'a' for Android on simulators).
Install the Expo client app on your iOS or Android phone and connect to the same wireless network as your computer. On Android, use the Expo app to scan the QR code from your terminal to open your project. On iOS, follow on-screen instructions to get a link.
Alastair and James had issues with Expo on their machines - after initially running fine, an error would cause Expo to stop and subsequently error (see below) upon further attempts at 'npm start'.
The only way we could get it going again was to delete the repo and git clone the project again. After much googling, we were able to find a fix that worked on James's machine, by deleting the .expo folder in our project repo whenever Expo crashed and running 'npm start' again.