Bad Twin was created in the LOST 'universe', then released as a real life tie-in novel. It is available in hardcover and audiobook.
Bad Twin was written by (fictional author) Gary Troup, who delivered the manuscript to Hyperion Publishing just before his fateful trip on Oceanic Flight 815. It is unknown if the author survived the crash, but the manuscript was found and read by Hurley (in Episode 2x13—The Long Con). The manuscript was later acquired by Sawyer. Before Sawyer could finish reading it, Jack burned the ending to emphasise his serious demand that Sawyer hand over the stolen guns (Episode 2x20—Two for the Road).
About the novel
The main character of Bad Twin is Paul Artisan. The book centers around Artisan's search for Clifford Widmore's 'mirror' twin, Alexander (the supposed Bad Twin) who has a personality similar to Sawyer's.
The note from the editors indicated that the author was lost when Oceanic Flight 815 crashed in September 2004. However, page 204 of the book details the main character learning of the ceasation of Scottish feudalism on 28 November 2004 (the factual, real-world date).
This anachronism indicates author knowledge of events that occured after penmanship, after delivery of the manuscript to the publisher, and after the date of the crash.
Sometimes evil has a familiar face . . .
Paul Artisan, P.I. is a new version of an old breed -- a righter of wrongs, someone driven to get to the bottom of things. Too bad his usual cases are of the boring malpractice and fraud variety. Until now.
His new gig turns on the disappearance of one of a pair of twins, adult scions of a rich but tragedy-prone family. The missing twin -- a charismatic poster-boy for irresponsibility -- has spent his life daring people to hate him, punishing himself endlessly for his screw-ups and misdeeds. The other twin -- Artisan's client -- is dutiful and resentful in equal measure, bewildered that his "other half" could have turned out so badly, and wracked by guilt at his inability to reform him. He has a more practical reason, as well, for wanting his brother found: their crazy father, in failing health and with guilty secrets of his own, will not divide the family fortune until both siblings are accounted for.
But it isn't just a fortune that's at stake here. Truth itself is up for grabs, as the detective's discoveries seem to challenge everything we think we know about identity, and human nature, and family. As Artisan journeys across the globe to track down the bad twin, he seems to have moved into a mirror-world where friends and enemies have a way of looking very much alike. The P.I. may have his long-awaited chance to put his courage and ideals to the test, but if he doesn't get to the bottom of this case soon, it could very well cost him his life.
Troup's long-awaited Bad Twin is a suspenseful novel that touches on many powerful themes, including the consequence of vengeance, the power of redemption, and where to turn when all seems lost.
An excerpt from the audiobook version can be found at the www.Soundsgood.com Bad Twin product details page. 
Factual Entities Mentioned
The book is listed as fiction, while mentioning 'real' corporations and people (related to LOST).
Connections to The Lost Experience
- See an interview on the author's page, and see also the Hanso Foundation advertisement and press releases related to Bad Twin
A MESSAGE FROM HUGH MCINTYRE, DIRECTOR OF COMMUNICATIONS AT THE HANSO FOUNDATION Don't Believe "Bad Twin" For over thirty years, The Hanso Foundation has stood for compassion and innovation, but today, our reputation has been attacked in the novel "Bad Twin", written by Gary Troup and published by Hyperion books. Throughout the pages of "Bad Twin", readers have found numerous passages featuring misinformation about The Hanso Foundation and its partners. The Hanso Foundation strongly objects to the book "Bad Twin", and encourages readers to make up their own minds. The truth about The Hanso Foundation is available at www.TheHansoFoundation.org and not on the pages of Gary Troup's "Bad Twin". Experience it for yourself. Thank you, and namaste. (Hanso Foundation Logo: Reaching out to a better tomorrow)
A photocopied image with an identical message appears on letyourcompassguideyou.com. 
Theories and other Thoughts
- The "real author" that wrote Bad Twin is theorised to be James Patterson. The audio file provided by the online book company www.soundsgood.com (listed as a reseller on the Gary Troup website) provides a © (copyright mark) for James Patterson. ABC made a press release that they had hired a well-known mystery author to write the book. James Patterson wrote Along comes a spider and Kiss the girls, which both became major motion pictures.
- Another theory is that the author is Stephen King (a known follower of the show) or Dean Koontz (cited reason is frequent similarities in syntax and writing style).
- The book seems to be a conspiracy theory based around the Hanso Foundation, similar to the Da Vinci Code and the Catholic Church.
- The book is published by Hyperion, who according to greek mythology was the son of Gaea (goddess of earth) and Uranus (god of heavens), and was the father of Helios (the god of sun who drove his chariot across the sky east to west on a daily basis). In further Greek mythology Helios (the sun) informed Demeter (goddess of earth) what happened to her abducted daughter Persephone.
- It is unknown whether the published novel is the same as the version in the typed manuscript on Flight 815. There may have been multiple manuscripts, or the publisher published an earlier draft submitted by Troup.
- Currently on the final season of "Alias" - another series, like "Lost," created by J.J. Abrams - heroine Sydney Bristow is battling a "bad twin," a nemesis genetically altered to look like Bristow.