Hold The Timeline

A tower defense game where the only resources are a few seconds that are always ticking away. Building defenses uses time. Enemies take time and give up time when they die.

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Time travelers have determined that they can use our planet as a "slingshot world". Going through our world gives their time travel machines more power. They build portals in high speed areas without permission.

Every time they use our world for their machines, they steal time from our dimension. Our survival relies on stopping them.