Worlds United is The Design Mechanism's venture into the world of the pulp adventure genre.
Imagine that the Solar System had turned out exactly the way Twentieth Century science fiction authors had imagined it. Venus as a humid jungle planet, Mars as the home of a dying civilisation, and rocket ships routinely travelling between these worlds and the Earth.
Even a Moonbase or two, if you like.
Now imagine a world where a cataclysmic event had caused humanity to take to the stars -