I just finished reading Dies the Fire by S.M. Stirling. Set in the same universe as his Nantucket Island series, it posits what happens when an outside event causes all electrical equipment and steam engines to stop working (it also throws Nantucket back in time). This series is set in the rest of the world in the modern day. Everything is reduced to medieval technology. The main characters have to learn to adapt to that world. It’s been a good read and I will definitely read the rest of the series.
One criticism of the book made by others was that he seemed to promote Wicca and downplay Christianity. I didn’t see any real slamming of the Christian religion, but the whole Wicca thing got tiresome after awhile. Still, if it had been a fantasy novel using a religion like that, it wouldn’t have bothered me, so I just kinda skimmed those parts. It IS a fiction book, after all!