are there any interesting books where a traveler from earth goes to some fantasy world and makes changes in the fantasy society with their "modern" ideas, either accidentally or on purpose? not just from the future to the past like in twain's book. i must be getting old, because when i was reading a book series where music causes magic to happen and found i was way more interested in the heroine's attempts to institute a postal service and double-entry bookkeeping for her accountants than the actual magic fights.
Inversions, from Iain Banks Culture series - well, very probably, since the book's perspective precludes 100% certainty that it is what it looks like, Culture intervention in a pre-modern society - probably fits your bill to some extent. Although the Culture take on interventions is sort of a more pro-meddling version of ST:TNG, so not so robustly "let's invent ALL the things!" as was the case in Twain's novel.
You're talking about the Spellsong Cycle by L. E. Modesitt Jr, I presume? That's his thing, he does minutiae like those things really well. There's a lot of military pulp SF that has a protagonist who either is from a futuristic time himself (David Weber's series) or has an adviser from same (Conqueror &c, by I think S.M. Sterling?). There's some other stuff, I'll try to remember it. It's one of my favorite genres. ^_^
This isn't exactly what you're asking for, but it SORT OF has to do with Time Travelling; Ilium, by Dan Simmons. Like I said, not specifically even kinda close to what you're suggesting, but still a fantastic book with some of the same ideas. Olympos, it's sequel, is also fantastic.
More military pulp stuff, I don't remember the name of the book or series, but the idea is that a regiment of troops from the north in the US civil war gets warped to another planet, surrounded by Russian medieval culture of sorts. Then the natives show up and it gets hilarious. Most of the stuff is really pulpy military SF / Fantasy, simply because the tech vs overwhelming numbers / preexisting advantage balance generates interesting interaction. See also the Belisarius series by whatever Baen writer. I like a lot of pulp, can you tell?
William R Forstchen, The Lost Regiment. First novel is Rally Cry. Loved it back in high school, doubt I could read it again. Charles Stross's Merchant Princes gets into society-tampering in a big way, as the protagonist decides the parallel world needs a hefty dose of egalitarianism. Not his best work, but worth reading. Bonus points for one of the antagonists being a
Your post reminds me a bit of what Pratchett has been doing with his Discworld series, gradually adding and re-imagining modern inventions in a traditional fantasy world. Recent additions included fiat currency, a modern national postal service, a telegraph communications analog and more recently the beginnigns of an underground train network. The biggest such examination though, carried through multiple books, is what happens when you mesh very modern ideas about policing with a fantasy world. There's no time travel element but I think it still provides the kind of thing you're looking for.
I was with you up until the part where you said Olympos was fantastic. I like most of Simmons work, and Ilium was fantastic, but it wrote a check that Olympos couldn't cash. If you can stand to read him, Piers Anthony's Blue Adept series melds a futuristic sci-fi world with a fantastical medieval one. The first 3 books of that series are probably some of his best works (which granted, isn't saying much).
The Anubis Gates by Tim Powers features both a time traveller heading backward and using his foreknowledge of the future do his advantage AND has strong fantasy elements, but isn't set in a fantasy world as such (instead 1800s London).
SM Stirling has a trilogy about the residents of Nantucket Island who get zapped back to the Bronze Age, and proceed to totally interfere with history. They're not too bad. First book is Island in the Sea of Time.
There was a series of books either by Robert Howard or by one of his contemporaries: Pulp medieval warfare books, very gritty (lots of sex, torture, and gore). One of the main characters was from the future, a Vietnam vet, or something. Last time I read those was in middle school. Joel Rosenberg had a series of books from the mid 1980s about a group of people sucked into their own Fantasy RPG setting (Guardians of the Flame, a series of books). The only reason I wouldn't suggest them is that I met Joel on a number of occasions, and he's a bonafide asshole. I suppose C.S. Lewis' Narnia series qualifies for this sub-genre, as well. There was a Reddit thread a while back that spawned a movie script based on an author's ongoing updates: A modern military unit gets sucked back in time, and gets stuck during the height of the Roman Empire. It was called Rome, Sweet Rome, and has been picked up to be filmed.
Also, the Warlock series from Christopher Stasheff. Starts with The Warlock In Spite of Himself. Basically: An agent of the intergalactic government flies out to a planet that's a medieval backwater, and discovers that folks there have magical powers.
A Fire Upon the Deep by Vernor Vinge. Highly advanced humans crash land on a planet with a relatively primitive alien species (iron age-ish, if I remember right), and end up jump-starting a lot of technological development. A Deepness in the Sky, his second book in the same universe, has some similar themes. The third book, The Children of the Sky, is a direct sequel to the first one.
The definitive answer to this question IMO, is "Lest Darkness Fall" by L. Sprague de Camp, which is both on point and a classic of the sci-fi genre. Highly recommended. Here is a collection with the classic plus a few more recent knockoffs. I haven't read the newer stuff but Lest Darkness Fall is great. Oops: didn't read the entire OP. This is time travel, not fantasy, but still damn good IMO.
I have exactly the series for you, also by L Sprague de Camp: the Enchanter stories. The modern-day protagonists journey through mythological realms (from Norse to Celtic), armed with their knowledge of everything from story logic to how to make whiskey. I read it when it was a teenager and it was cracking good fun. I respectfully but strongly disagree with ehm ecks ' suggestion of Charlie Stross' Merchant Prince novels. I keep meaning to necro the 'otherwise promising writers who go off a cliff' thread with my rant about that series, which starts promisingly, but derails so very hard. This was the series that made me go from "buying every Stross book" (I even got them autographed!) to "never buying/reading anything by Stross ever again". D:
I fail to see how Actually, I hope you do get around to posting that rant. My critical faculties tend to disengage while I'm consuming a work (movie, TV, book, whatever) that I like, so other perspectives are always interesting.
I liked it. I guess I understand if you didn't. It wasn't the best, but I fully enjoyed having that ending, and the moravec storyline was great.
