All the time. Most of my fiction is the result of a challenge of some sort - either I challenge myself to see if I can write something, or someone else issues a challenge that I decide to jump in on.
After listening to several (mostly bad) system and isekai stories, I challenged myself to write one, leading to Digital Cowboy Dane. (Pocket FM)
A challenge I no longer recall led to the opening scene in Strange Awakening, and the idea kind of sat around for about six years with just five hundred words until I acquired a game called Mighty Protectors and generated a character that was strangely close (I think even to "male character in female body") to the character I'd written that scene about, so I made it a superhero story.
Twice I toyed with creating a "hard-boiled detective novel" but with a superhero as the MC - and had four halting beginnings. Have never gotten past chapter one with poor Timothy Browne, the dhampyre detective, but Jack Diamond has one (short) novel, the start of another and a few ideas in note files.
Someone posted an idea here about the most ridiculous System concepts we could come up with, and the idea for "The Kaiju System" (Honeyfeed) was born.
My other stuff has a bit more complicated origins (often spanning several years or decades, like Strange Awakening did). True Blue was a television series in the Omniverse, a "shared world" designed using the rules for the Champions Super-Powered Role-Playing Game (4th Edition) for an Amateur Press Association (kind of a hard copy version of a discussion forum), about a character who died fighting an alien invasion in the setting background. Originally it was going to be a comic book (I'd even toyed with using a digital design suite I had to do some actual pages for it, but that was just TOO ambitious at the time) that one modern Omniverse character was reading to her much younger siblings while babysitting them, with some breaks for her to do stuff, either with the kids or in her own heroic ID, and the first two pages were initially written as a script (without the short "narrator" bit). At the end of that story, the character reading the book was going to have a brief reminiscence of seeing the show on television, and having watched it with her uncle, who had been one of the police officers at the diner in the (in universe) real-life event used for the show's pilot (and for the script of the comic), giving it far more impact, especially at the Big Reveal... And, of course, this was also supposed to be done a couple of months before that dead hero apparently returned... and his heir, Legacy, also showed up...
Between Worlds (Between Earth and Pyrroth on Pocket FM) is just an attempt to do an epic fantasy/urban fantasy crossover. The list of stories inspiring it is longer than this thread, including my post.
