There are some real tower defense gems on Mac, from PixelJunk Monsters Ultimate to Kingdom Rush and Plants vs. Zombies, but Protolife brings a compelling twist to the formula. Here, you’ll defend a space colony on the planet Gagarin-5 from a sudden infestation of a rapidly-growing organism, which you’ll do by building up defensive towers using a single, small robot.
Rather than drop in prefab towers, you’ll build them block by block. That offers more flexibility and customization, but also requires more tactical thought as you contend with the uncommon threat. Protolife includes more than 30 levels, and the lo-fi pixel aesthetic seems like a neat way to convey this intriguing space conflict. You can buy it on Steam.