Both the main game, Antecedent, and companion app, Lockbox, are required to complete the game. The main game is PC-only, while the companion is available for both Android and PC. The zipped folder at the bottom of this page contains everything you need.
The companion app can also be downloaded from Google Play here: play.google.com/store/apps/details?id=com.greenvalegiants.lockbox&hl=en_GB
The game's source files can be downloaded here: https://drive.google.com/folderview?id=0B4DAOWloayaTbXVBX19iVFdXZGc&usp=drive_web