You can't argue with a free 4X strategy game. You also can't argue with a free Warhammer 40k game either. Luckily enough then, you've still got a few days to redeem Warhammer 40k: Gladius - Relics of War for free on any of the major PC storefronts. The grimdark sci-fi of Space Marines picked up the core tenants of explore, expand, exploit, and exterminate a few years ago, and now you can own it on Steam for free.
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Warhammer 40,000: Gladius - Relics of War puts a hex-based 4X spin on the setting