I just use a spreadsheet for everything. Google Sheets is great, but in keeping with the spirit of the Fediverse, EtherCalc is a less-corporate alternative. If being in the cloud isn't needed, Gnumeric is my go-to spreadsheet; it has a portable version for Windows and doesn't need to load a whole office suite to open up.
Playing Tabletop Roleplaying Games Alone
Welcome to the SoloRPG community!
Some people prefer to play their tabletop roleplaying games alone, to avoid the drama and scheduling issues of traditional group games, while others play solo because they're unable to find a group to play with.
Whatever your case may be, you're more than welcome here to discuss your experiences as well as ask any questions that you might have.
For an introduction to this style of play, read Why Play Roleplaying Games Alone.
This is a very interesting question. Unfortunately, I don't have an answer (interesting or otherwise). I do my prep in a desktop text editor called Emacs with the org-roam extension, but that doesn't fit with your requirements unfortunately.
I’m just starting what I hope to be a long-running hexcrawl oriented game (I’ve been streaming my prep) and the one app that I’m leaning heavily on right now is a digital whiteboard app called Weje. I find it very useful to organize and gather information.
https://rolescape.io/ is a fantastic tool for GM-Prep as well as solo-rpging, everything from characters to locations to events is easily referenced. If you want the whole experience with character sheets and (virtual) dice, my answer is foundry vtt. Their module for Ironsworn / Starforged is top tier.