Self e-published, 2010
Luminosity is a rationalist fanfic based on Stephenie Meyer's novel Twilight. And yes, if any of that makes you want to stop reading, you might as well give up now. However, within those constraints, it is quite good.
The story is very closely paired to the original novel, using exactly the same characters, setting, and timeline. Lines and whole paragraphs are lifted directly from Twilight. For the first few chapters, Bella is going through exactly the same movements, meeting the same people, and holding the same conversations -- only her internal dialog is different, with more self-analysis and less social anxiety and negative thinking. This is an interesting way of writing an alternative storyline, allowing us to see the differences that small changes in behavior have on the story... but it would be more interesting in a setting that involved more than dealing with a rather boring high school. This starts to change rapidly in Chapter 3, when Bella figures out that something very odd is going on, and manages to force the Cullens to reveal themselves as vampires.
The plots diverge quickly thereafter, with Bella discovering pretty much everything about the vampires in the next few chapters, information that is spread out over the entire original trilogy. What doesn't happen is all of the sappy romance stuff... well, most of the sappy romance stuff, anyway. Instead of obsessing over Edward, Bella actually talks to the other vampires, takes a proactive role in directing her life, and, of course, insists that immortality is a gift best not delayed.
It has been a long time since I read Twilight, and in order to keep tack of the changes I read the two works in tandem. An interesting effect of reading the stories in parallel is that the original novel comes across in a better light. In either book, Bella's character is a responsible and intelligent person, something that is easy to forget when you hit the mushy bits in the original books. However, even these small differences manage to add up and pretty much rip original the plot to shreds.
As a work of writing and as a fanfic, Luminosity is well-written and engaging. While it would not be bad as a stand alone work, I would not particularly recommend it unless you have already read and enjoyed the entire Twilight series. I don't really see it as a shining example of rationalist fiction; it is generally consistent with rationalism, but it doesn't have the "wow,that's clever" vibe that much rationalist fiction has.
At the risk of mild spoilers, I think that it is relevant to mention that the end of this book is just plain depressing. Like, really depressing. But the story continues in Radiance, which is less depressing.
You can read both books here.