Old Mortality: Tillietudlem, Lady Margaret's castle, is fictional but possibly inspired by Craignethan Castle. Years later a railway station and a small village in South Lanarkshire were named after Tillietudlem.
The CD From the Discworld by Dave Greenslade, which mostly consists of Disc-themed instrumental peices, has two songs. One is an original song about Ankh-Morpork. The other is a defictionalisation of Nanny Ogg's second-favourite song, "A Wizard's Staff Has a Knob on the End". (It could have been worse; it could have been her favourite song.)
Around the time the movie adaptation of John Irving's novel A Widow For A Year came out, the children's book A Sound Like Trying Not to Make a Sound (featured in the novel and the movie) was published for real.
A George Orwell essay describing the "Moon Under Water", his idea of a perfect British pub, inspired (at least in theory) the creation of the J.D. Wetherspoon chain. A number of Wetherspoon's pubs are indeed called the Moon Under Water, and others have "Moon" themed names.
One of the novels of Kurt Vonnegut's fictional author Kilgore Trout was Venus on the Half-Shell. Philip José Farmer later wrote an actual novel title Venus on the Half-Shell that he published under the pseudonym Kilgore Trout. note Some critics thought Kilgore was Vonnegut and the book a "worthy addition to his canon" pissing off Vonnegut no end, even though he had given permission to Farmer to use the name.
In Time Enough for Love by Robert Heinlein, the Framing Story is that the main character, Lazarus Long, is reluctantly recounting his life story. The computer recording his recollections is instructed to select quotable portions and compile them into a book of his quotes. These are presented within the book in interlude sections. However, in 1978 and 1988 actual books were published of only the quotes.
The Necronomicon is listed in the Ohio University Library card catalog. L. Sprague de Camp, fantasy author and linguist, acted as Abdul Alhazred's "translator".
There are even a few published books calling themselves the Necronomicon. Most are little more than black-magic occultism books that will make passing references to Cthulhu at best, and no reference to Lovecraft at all at worst. The most famous is the Simon Necronomicon, but one that is closest to what the fictional Necronomicon contained is probably Necronomicon: the Wanderings of Alhazred, as written by occult writer Donald Tyson.
In the novel The Amazing Adventures of Kavalier and Clay, the protagonists create a comic book series called The Escapist. Then a 6-issue miniseries came out, printing various comic book stories from The Escapist, from the '40s through the present, with explanatory articles by real important figures in the comic book world, about the series' various publishers, and its place in the changing trends and values in the history of comics.
Telegraph Avenue had a record store featured in the book defictionalised as part of the book's advertising campaign. An article on the campaign even cites this page.
The The War Against the Chtorr series features the Mode Training, which is kind of self-help training on acid. Guess what? David Gerrold, the author, is building an actual Mode Training program. Oddly, one of the books has him set aside some pages to point out that Mode Training is fictional and he never wants to see anyone creating "Mode Training" and charging people money for it, because it was rather dangerous. Perhaps this meant other people.
Several segments of the titular play of Robert W. Chambers' short story collection King in Yellow have been later written by other authors. Thom Ryng is the possibly the only one who has not only written the whole thing, but also had it actually played on stage. No reports of insanity have been made of the readers, but save for a few anachronisms in language and style, it's a very good and suitably bleak story of how You Can't Fight Fate in a world inhabited by monsters.
The Dragonlance Chronicles and subsequent campaign setting use the Inn of the Last Home as a starting point, which is known for Otik's famous spiced potatoes. Enthusiastic Dragonlance fans have created several recipes for the potatoes and one such recipe was listed as a notation in the Annotated Dragonlance Chronicles.
In Dragonlance: The New Adventures, Sindri writes a guidebook titled A Practical Guide to Dragons, which is mentioned In-Universe in the Suncatcher Trilogy. It was published in real life just after the first book of that trilogy.
Andrea Camilleri's books are set in Vigata, a fictional town in Sicily, which is based on Porto Empedocle (Camilleri's birthplace) and Licata. In 2003, the city administration of Porto Empedocle added the fictional name to the tourist signs, which would then read Porto Empedocle Vigata, without actually changing the city's name. The decision has been reversed as of 2009.
The film Boys & Girls Guide to Getting Down is in a strangely similar format.
Orson Scott Card wrote a book called Speaker for the Dead, in which the speaker researches the life of the deceased, then tells the deceased's life story as they would have told it. According to OSC, people have started doing this in real life, and apparently, it is a very emotional experience.
"Poohsticks", introduced by that name in A. A. Milne's Winnie the Poohnote and portrayed in the Disney short A Day for Eeyore is a simple game doubtless imitated by many readers/viewers who come across it: Drop two sticks (or fir cones as were first used) into a river on one side of the bridge, first one out on the other side wins). Who'd have thought it could lead to an annual World Poohsticks Championship though?
Sherlock Holmes famously lived at 221B Baker Street, which was turned into an actual address and is now a museum for Holmes fans. (Originally, Baker Street didn't extend far enough to have a #221, which is no doubt why Doyle chose that number.)
Michael Muhammad Knight wrote a book called The Taqwacores about a then-fictional Muslim punk scene. The idea struck the fancy of a number of punk-minded Muslim kids who proceeded to actually bring the Taqwacore scene into existence.
Icehouse, the game and game system from Looney Labs, started out as an idealized fictional game in Andrew Looney's short novel The Empty City.
Goosebumps: Goldberger Doll corporation started manufacturing and selling real Slappy the Dummy ventriloquist dolls after getting a request from a young fan.
The Arthur C. Clarke novel The City and the Stars begins with our heroes playing a virtual reality adventure game. This wasn't a new concept, even in 1956 when the book was published. However, two small details indicate that Clarke thought the concept through more than his colleagues: the game contains a bona fide Quest Arrow showing our heroes where to go; and Alvin causes the game to crash by attempting Sequence Breaking. After the game crashes, the other players (who are each in their own apartments, connected together by a telecommunication link) accuse Alvin of constantly crashing their games. He honestly wants to see the scenery outside the dungeons they were adventuring in, but nobody thought to implement that, since Alvin is the only non-agoraphobic man in the city.
U.S. Robotics, a company that manufactures dialup modems, took its name from the fictional U.S. Robots and Mechanical Men corporation featured in I, Robot, though the company has never manufactured robots itself.
The Niven & Barnes novel, Dream Park has experienced two such attempts:
The Dream Park, a holographic LARPing theme park, was built as a fan-created corporation intended to establish the titular park. The organization unfortunately went bankrupt in 1999.
The novel's game-regulating organization, the IFGS, actually has been Defictionalized into a LARPing club that stages its games outdoors.
An in-universe example in Poul Anderson's "Critique of Impure Reason" — Tunny and Janet fake up a novel and its criticism to persuade the robot to go to Mercury and mine. But other people get wind of it, and at the end, Tunny rolls out the book for popular reading and hopes of a new fiction rennaissance.
In World War II, the US Navy took the idea that became the Command Information Center "specifically, consciously, and directly" from Doc Smith's Lensman novels.
In Snow Crash, the main character Hiro Protagonist uses a program called Earth, which later was an inspiration for Google Earth
Fan merch for the Dragaera novels includes copies of the menu at Valabar's, as per the dining scenes in Dzur. Fans of the series have sometimes attempted to reproduce the recipes as well, albeit with substitutions for things like goslingroot or rednuts.
In Lauren Child's Clarice Bean novels (not picture books) Clarice is a fan of "Ruby Redford" books about a schoolgirl super-spy. Due to reader demand, Child has since written several Ruby Redford books.
The popular sixteenth-century Spanish novel Las sergas de Esplandián described a strange, mythical land inhabited by beautiful Amazons. The name of this place? California. Spanish explorers named what they thought was an island (present-day Baja California) after the book. And five hundreds years later, California does have a reputation for being a strange land with beautiful women, though sadly not Amazons.
Robinson Crusoe: In the 1960s one of the islands near South America was named Robinson Crusoe Island as a homage to the novel in which Crusoe is stuck on a tropical isle.
Inventor and SpaceX CEO Elon Musk named two of the company's spaceport drone ships Just Read the Instructions and Of Course I Still Love You, after ships from Iain Banks' novel The Player of Games.
In the 1970s, the Romanian government made efforts to attract a larger number of tourists from Western Europe as a source of hard currency. They naturally received inquiries about visiting the castle from Dracula, probably the most famous fictional work set in the country. Unfortunately, Bram Stoker had never even visited Romania, and there had never been a castle at the Borgo Pass as described in the novel. So the Romanians built a modern hotel designed to look externally like a medieval castle, and promoted it as Dracula's Castle. It still exists as the Hotel Castel Dracula. To increase the spooky atmosphere, the hotel's grounds included a genuine local graveyard.
20,000 Leagues Under the Sea, published 1869, featured the fantastic idea of a high-tech submarine. In 1954, the world's first nuclear sub was named the USS Nautilus in honor of the book. It should be noted that there was at least one sub with that name before the book.
One of the Captain Underpants books has a look into George and Harold's origins as best friends and creating comics. One of their comics was known as Dog Man, and years later, Dav Pilkey himself wrote and published a separate Dog Man book!
In the mid-2000s Scholastic sold a version of the 3D Hypno Ring from Captain Underpants through their Scholastic Book Club Service. It even included an owner's manual with the warning not to dump water on the head of a hypnotized person.
The small French town of Illiers, near Paris, inspired Combray in childhood resident Marcel Proust's A la recherche de temps perdu. To make sure tourists know where to go for their madeleine moments, it has renamed itself Illiers-Combray.
The protagonist of The Princess Diaries "wrote" a romance novel called Ransom My Heart, excerpts of which were included in the tenth book. Then the author published the whole thing as a standalone book.
Ann Leckie seems to be a fan of this. When touring to promote each book in her Imperial Radch series she gave out pins to fans, like the Radchaai wear, and has offered a limited supply for sale on Etsy a few times. When promoting Provenance she signed vestiges.
The series includes a fair amount of Food Porn, so naturally some of its more interesting foodstuffs have been manufactured in the real world, including Butterbeer, Chocolate Frogs, and Bertie Bott's Every Flavor Beans.
Quidditch, originally a fictional sport exclusive to the series, recently became a real thing in 2005 when it was played in a Middlebury, Vermont game, though it became known as Muggle Quidditch to distinguish it from the fictional version. Then in 2015, a new [semi]-professional league was born under the name of Major League Quidditch, which is played primarily in the Midwestern and Northeastern U.S., but also has teams in the Deep South and Ontario, Canada.
Rainbow Rowell's Fangirl includes the fictional Simon Snow novels, an Expy of Harry Potter; the protagonist Cath writes a lengthy fan fiction about her own version of Simon's eighth and final year at school, called "Carry On, Simon". Rowell later wrote a full novel set in the Simon Snow universe called Carry On – however, the book is not "Carry On, Simon" itself: rather, it is Simon's final year if written by Rowell as herself, rather than as Cath or as in-universe author Gemma T Leslie. Carry On spawned sequels of its own, Wayward Son and the upcoming Any Way the Wind Blows.
Walter Tevis' 1959 novel The Hustler (adapted into the 1961 film of the same name) has legendary pool player Minnesota Fats as its antagonist. Actual pool hustler Rudolf Wanderone changed his name from New York Fats to Minnesota Fats after the success of the book and film. He then claimed that the fictional character was based on him, which Tevis and the filmmakers both denied.