ExoImperium: Space Tycoon

ExoImperium: Space Tycoon is an offline-first sci-fi strategy and factory
automation game. Colonize planets, build automated production grids, manage
interstellar logistics, research technologies and command battle fleets.

The Linux build includes the Imperial Store powered by PayPal. Purchases are
delivered automatically, including delayed payments: if PayPal confirms a
payment after you close the game, the credits and circuits are granted the
next time you launch it.