Direct link to APK file: https://github.com/btcontract/lnwallet/blob/master/app/app-release.apk

Genuine Bitcoin Lightning Wallet is ONLY available on Google Play store for now:

DO NOT install Bitcoin Lightning Wallet from other places!
This wallet uses modified code from https://github.com/ACINQ/eclair project.