Stonepunk
If cyberpunk is dystopian futuristic sci-fi based on computer and network technologies, and steampunk is dystopian futuristic sci-fi transplanted to an alternate Victorian age with modern-equivalent technologies based on the steam engine, and clockpunk is dystopian futuristic sci-fi transplanted to an alternate Renaissance age with modern-equivalent technologies based on clockwork, then stonepunk is … well, you get the picture. Imagine the assassins, flying machines, robots, and decadents of cyberpunk, in a setting where the highly advanced technology consists of stone wheels and rope. For a real challenge, make the technology handaxes. That’s not a bad one, actually. One day, a bunch of bad guys show up with sharp stones and establish dictatorial rule over all known civilization (i.e. the tribe and its two neighbors). Our heroes must make a perilous journey across the world, from the forest to the gorge, as they race against time to reverse engineer the previously-unimaginable fabrication technology behind this new superweapon.
The idea generalizes. You can think of the defining attribute of steampunk and related genres as being a deliberate projection back in time of a particular kind of science fiction. (There are other interpretations, and also lots of steam-, clock-, and whatnot-punk that don’t fit this reading.) But how about taking not just other time periods but other genres? Hard sci-fi offers lots of possibilities. Take the meticulous working-out of relativistic-speeds space combat, and imagine treating classical wooden-ships naval warfare in that tone. The conversation on the quarterdeck is all about the precise trigonometry of closing angles, and reloading intervals; reports come up from belowdecks that hull capacity is at 12%, and with one more hit, captain, B deck will be open to fluid! (Or, in the reverse, one could write about starships the way Patrick O’Brian wrote about sailing ships.)
The Recreation of the American Republic, or, If Thomas Jefferson Were Alive, He’d Be Two Hundred and Sixty Two
Someone develops the technology to raise the dead in new bodies, and for reasons that can easily be invented, decides to bring back to life the major Founding Fathers. They’re now stuck in 21st-century American; hijinks ensue. Franklin is the first to really adjust (he did want to be dropped in a barrel of Madeira and brought back when technology would permit, after all), and immediately sets of wheeling, dealing, whoring, and inventing. Jefferson is profoundly uncomfortable, and while he can be charming in conversation, when left alone he goes back to moping about what seems to him a hideously industrialized world out of touch with its virtuous agricultural roots. Eventually, though, Washington and Madison talk him into shouldering his burden and teaming up with his old enemy Hamilton to track down a shadowy figure who is somehow using the revived Framers to bring down the United States. The Jefferson-Hamilton team, mismatched and distrustful of each other, must nonetheless use their very different intelligences and skills to prevent the resurrection of a zombie army of evil invincible redcoats. In the shocking surprise ending, Hamilton must redeem his honor by defeating the revived Burr in a rematch in of their duel in a much-changed Weehawken, while Jefferson, across the river in a deserted basement of the old original Federal Hall in New York, must talk a fanatical Patrick Henry into releasing the kidnapped Franklin, whom Henry has been forcing to develop the advanced resurrection technology necessary. Anachronistic, silly, and a total page-turner.