Most of these books involve a complex system of a limited number of linked parallels and people who travel between them, sometimes using technology and sometimes magic. The most heavily technical is A Tale of Time City, which concerns a city outside the regular time-stream, with machines which are used to regulate the parallels and stop history drifting too far out of true - but there's still a strong magical element involved.
The most off-beat is The Homeward Bounders, in which our world, and other parallel worlds, turn out to be being run as a vaste RPG by extra-dimensional beings, and anybody who discovers this secret gets thrown out of their own world and left to try to find their way back through randomly scattered energy-portals which are more likely to lead them further astray. You can call the gamers aliens and call the story SF; you can call them demons and call the story Fantasy.
The hero calls them demons - but then he is a mid-Victorian child, at least initially (homeward-bounders are immortal until they find their own world), so he wouldn't know the term "energy-being" if it bit him in the ankle. Various characters from earth's mythology appear in the story - Prometheus, the Wandering Jew, the Flying Dutchman - but since the first was really imprisoned not for bringing fire to man but for finding out about the demon-gamers and trying to warn people about them, and the last two are just very old homeward-bounders, you can still take the whole thing equally well as technology or as magic.