Any writer-- especially a genre writer-- is going to have a lot of notes. Character notes, story notes, location notes, worldbuilding notes, etc. etc.
Keeping track of that all can be exhausting. I use notes in Scriviner, I use Evernote, I use Excel spreadsheets, I use Photoshop for maps. I code everything with a three-letter tag for the series and a two-digit identifier for the entry in that series. For example, The Thorn of Dentonhill was VER01 (First Veranix book), and A Murder of Mages was MCI01 (first Maradaine Constabulary Inspectors book). Right now I have seven "active" project codes*: four
Since I'm constantly working on different things, I have a lot of things open at any given time, and the notes, spreadsheets, etc. for those things are incorporated.
So, a snapshot of what I've got open right now in all my various works in progress and secret projects.
VER03: Third Thorn book, which is my "primary" project right now. Thus I have with it all my city of Maradaine notes, maps of the city and of Aventil explicitly, a Dramatis Personae and outline breakdown for this book, and my notes on Tetchball.
BAN01: My still-in-progress space opera. In addition to the manuscript, Dramatis Personae and outline breakdown, I have notes on the main alien races, as well as the various others which are part of the larger universe but not involved in this story. I've got the 10,000+ stars of the 'verse on a monster spreadsheet, and some photoshop files that attempt to visualize the 3-D starmaps in a way that makes sense.
MSD01: Secret Project #1. Still very much in the early work-in-progress stages, with the requisite Dramatis Personae and outline breakdown, as well as maps, worldbuilding notes on places and flora and fauna, and a long-term plan for that. There's always a long term plan.
9DE00: Secret Project #2. It's a "00" because this is something fully in the worldbuilding/planning stage, not actual-manuscript stage. Here I've got maps-- oh so many maps-- and culture/worldbuilding notes in progress. I have a lot of linguistic notes, including an excel file with fifteen different phonemic inventories. I have history notes-- still very much in broadbrush-- and the beginnings of character notes. I still don't know entirely what this is going to be or the shape it'll take, but I am very excited about what I'm doing with it.
*- Actually, technically, eight, but that eighth one is a Long Plan thing, not something I'm currently writing in any way.