A ”popular” variation on the Alternative World is one in which the Nazis won World War II: these includeThe Sound of His Horn by Sarban (John William Wall, 1952), The Man in the High Castle (1962) by Philip K. Dick, The Ultimate Solution (1973) by Eric Norden, SS-GB (1978) by Len Deighton (1978), Fatherland (1992) by Robert Harris, December 7, 1941: A Different Path (1995) by David L. Alley, 1945 (1995) by Newt Gingrich & William R. Forstchen, In the Presence of Mine Enemies (2003) by Harry Turtledove (2003), Amerikan Eagle by Alan Glenn (2011), The Afrika Reich (2011) by Guy Saville and Dominion (2012) by C.J. Sansom (2012).
Katherine Burdekin‘s feminist sf novel Swastika Night (1937) is set in a future where Hitler was victorious but is not, strictly speaking, an ”Alternative World” novel as this was a real possibility when the novel was written.
A modern trend in Alternative World stories is Steampunk.
H. G. Wells‘s The Time Machine (1895) and The War of the Worlds (1898) has inspired a number of pastiches set in worlds where the Time Machine was, in fact, invented, and/or the Martians invaded Earth in the early 20th Century: such novels include Christopher Priest‘s The Space Machine: A Scientific Romance (1976), Morlock Night (1979) by K. W. Jeter and The Time Ships (1995) by hard-sf writer Stephen Baxter.
Radically Alternative Worlds
Some Alternative Worlds differ from our own at a more fundamental level, for instance Alternative Universes in which the laws of physics are different.