I was working on my latest client project in rails when I had an idea. You see, for years I have been writing / revising / researching my novels, and I've accumulated heaps and heaps of papers documenting all of this "stuff." I might be a bit unusual, but I actually care that if/when I reference a "holy book" in my novel - I actually have a mostly-written version of that book available to reference. I don't just "make up crap" and toss it into my novel without another thought. I mean, I wouldn't just toss in any old spice I grab from the cupboard into whatever I'm cooking...
So I document everything. I have a language, with characters, grammar, usage, dictionary, etc. I have a recipe book that records the kind of food I serve to the people in the novels. I have an encyclopedia (or did) that references flora, fauna, culture, habitat, environment, planetary system, solar system, constellations, etc. I have religious texts, etc. I literally have hundreds of thousands of pages of all of this crap - on physical media.
As anyone that writes knows, having all of this stuff on physical paper is a nightmare to track. Where the hell is the note I wrote fifteen years ago in that one notebook about the *THING* that I'm trying to remember?! Didn't I just make another chapter in the religious text of the people that are on the green side of the religious debate?! Has anyone seen my sketch-note book that has all the information about architecture in it?!
Uh huh. This is the state of novel affairs. So, I was working when I thought, "this would be so much better if I just had a single place I could store all this crap digitally, reference it, search through it, and of course, MAKE BACKUPS." (*Note to self: when packing your belongings for the 405th time, please take note of things like "little post-it notes that seem to be stapled together," BEFORE throwing them in the rubbish bin.)
So, I keep picturing the following pieces (granted, this particular idea works for me, and may not be the core of what someone else needs... but at least it's modular.):
Dictionary - create/edit/delete/view/search of words, definitions, parts of speech, gender, declensions, plurality, synonyms, antonyms, root structure, and of course a reverse-captcha to actually show what the word looks like with native character images (until I can be be arsed to make a true font... argh.) The definition text could certainly benefit from something like markdown or textile markup as well.
Reference Bookshelf - create/edit/delete/view/search for "books" like this world's history, their cosmology, biology, religion, and encyclopedia. Each book would have a title, then inside would be comprised of chapters or sections, and pages, possibly sub-divided into further sections. Pages would definitely benefit from page-numbering, chapter or section numbering, tags, and some kind of markup as well.
Notebook / Scrapbook - create/edit/delete/view/search for notes or scraps - which are comprised of a subject/title, a body, creation date, and tags. If I can include multimedia along with text than these scraps/notes are like a doubleplusgood version of postit notes. Having the ability to markup text and tag each scrap/note makes them organized in a mind-map kind of way, without having to think about the structure before I create each scrap/note. This reminds me of creating a blog article, actually.
Writing Area - create/edit/delete/view/search for actual drafts of my novels. This area is remarkably similar to the reference bookshelf, but for my purposes is exactly defined as being a book title, section name, scene number, key title, code number, draft text, and tags. Every "page" is arranged by code number (which is something like book-number.section-number.scene-number: 1.1.13) The draft text portion of this area will definitely need markup text.
The Dictionary, Reference Bookshelf, and Writing Areas all act like wikis. The Reference Bookshelf and Writing area have inherent organization to them in the idea of page numbers or code numbers, whereas the Dictionary is simply "alphabetized." The Notebook/Scrapbook acts like a blog without any kind of organization other than tagging/dates. So, I just need to create a nifty little ror app that does two things - a wiki and a blog, and has them separated into four sections to store the different kinds of information.
I even have icons. :) And that's the most important part, right? the visual design, of course.

So yay, I have a cute little application started to keep track of all my crap. Now I just need to map out some functions, get the feel of a couple of cute plugins, and it's all good. Yay for world creating.