In “Rumfuddle” a scientist has recognized that there are an infinite number of universes, and constructed a machine which can open portals between universes at a negligible cost. By opening portals to universes similar to our own (cognates, he calls them) he has ushered in a post-scarcity society: if petroleum, or lumber, or any other natural resource is required, simply travel to a universe which is just like ours, but in which humans never developed on Earth, and extract all the material you need. Social problems resulting from population pressure are solved: every family, every individual, if they so choose, can have a cognate Earth of their very own to live on. Because the machine can also open portals across time, scientific and historical puzzles are resolved: a paleontologist can travel to the Cretaceous of a universe almost identical to ours to observe dinosaurs first hand, a classicist travel to Ancient Rome, and the like.
As he often does, Vance uses his setting to present a tale of bizarre crimes and summary justice, highlighting the failures of the conventional authorities and their rules and the quest for answers and/or vengeance of a determined victim. As the story proceeds we learn of foolishness and abuses among the new elite raised by the "game-changing" new technology. The scientist who invented the dimension travel machine has authorized access to it to a group of people, the "Rumfuddlers," who have been using it to stage elaborate and theatrical jokes. By kidnapping and switching babies between dimensions they have, among other projects, produced the spectacle of Hitler and his henchmen working as staff in a kosher restaurant and Marx, Lenin and Stalin living as servants to Czar Nicholas, and organized a champion football team made up of such luminaries as Machiavelli (as quarterback), Achilles, Hercules and Richard the Lion Hearted.
This is a good story, combining Vance’s usual concerns with a “sense of wonder” of infinite possibilities and time travel. Definitely above average when compared to SF stories as a whole, but just average for Vance.