Android Studio with Scala plugin is required if you wish to compile it yourself.
Link to APK file: https://github.com/btcontract/bitcoins/blob/master/app/app-release.apk

Simple Bitcoin Wallet is available on the following app stores:
F-Droid: https://f-droid.org/repository/browse/?fdid=com.btcontract.wallet
Google: https://play.google.com/store/apps/details?id=com.btcontract.wallet
Xiaomi: http://app.mi.com/detail/105943