I’m looking for something easy to use. Something that I can have a folder for each chapter, and maybe sub folders in the chapter for quests, NPCs, locations, etc,

Possibly even an app that I can link information to the party to view, whether it be maps, letters, or other clues.

What do you use?

If you're DMing solely online I've actually just been using Discord. This way I can control who has access and when, there are spoiler tags, and it can be organised to three levels of granularity: Categories, Channels, Threads

Here you can see a glimpse of my server. I have two ongoing groups and a few one-shots going on. Let's look at my 'Lakeside' Group. They're D&D and so should make it easier.

If you look at the left of the image you'll see the category [Campaign] - Lakeside Group. That is basically where you would find everything to do with that game group. Then I have channels for different stuff. At the moment the image is open to the world's setting information. So everything you need about the lore of the world, the NPCs the party has met - it's all there. 

as you can see there's separate threads for the different information. You can see the early threads are about the setting's geography and basic background. Open on the right hand side is a recent thread of lore-heavy notes that the party found in an NPCs house. These are uploaded in the thread as images.

Another thread example is the NPC thread where I pop the information for noteable NPCs that the party have encountered:

Given that we run our online games from this discord server anyway (voice and video) with Owlbear as the VTT it just makes sense to have everything in one place. It can be viewed by players when I'm not online, I can set permissions for categories, channels, and threads meaning that only the people who should be able to see something can see it. And for anything else there is a spoiler tag within discord that allows you to hide bit of information that might be too meta for some players and give them the choice of when to click and reveal the information. 

I recently gave a player a private bit of information that his magic item would reveal the next time he used it. I hid the info behind the spoiler tag and so it was up to the player when they felt it was appropriate to click the tag and reveal the information. 

It's not a perfect approach I know, but it's an organisation that is the best I could replicate from my Filofax organisation for in person games - yes I'm old enough and nerdy enough to still use a filofax as a notebook and organiser! It seems to work well enough though, and my players haven't yet vocalised any issues with the system.

I should say though that for in person games - nothing beats a physical notebook. My filofax is still the best method of organising that I have. It allows me to move notes around, it allows me to use dividers to separate stuff. I even have the plastic wallet inserts so that I can store handouts and other print offs. It's my perfect solution.

I use Obsidian and Google docs or an old notebook that has seen better days for all my organization needs. Also what's Filofax?

I’m trying obsidian. The note taking part is pretty nice and easy. I was watching a video on some community made extensions though and that went over my head. 

There was one nice extension that I used that turns the text to look like a 5e book, loving that.

Scrivener is a tool for writing documents, but it covers the folders and sub-folders part nicely, and it has two panes so you can see two pages at the same time. However, it's probably not the ideal tool for this specifically, compare to a tool specific for dungeon masters. And I do not believe you can share things with the party with that app (but you could likely use Discord for that).

I also use Scrivener. It's not free, but you can organize the shiznit out of your info. And you can divide up the screen so you can see multiple documents at once. But that's just the tip of the iceberg. It's a GREAT note taking app. The major Con is it is local and not synced up to a cloud storage. I have mine set up to save to my Google drive, but to access it from another device, I'd have to have Scrivener installed. Oh yeah, no mobile either. But if you use one machine mainly and run your games from that same computer, Scrivener is great. I've been using it for years.

It uses a "tree" setup for document organizing. On that tree (the Binder) you can create all kinds of folders and categories. You can change icons to make it a little more visual. I add new icons all the time. I just go to flaticon.com and download a free png and then upload it into Scrivener. 

It has a really good search function too! If you are doing edits, it has a great Find and Replace function. You can customize the look of the interface to your liking. You can upload images and PDFs. There's a lot more it can do, but don't be intimidated. It's primary and most basic function is being a word processor (typically for writing books). It might have a little of a learning curve, but not really. I just learned as I used it more. I've been using it since 2012.

Totally worth the price you pay.

There's no sharing per se, but depending on what communication platform you are using, you could feasibly use screen sharing I suppose.

Good luck!

I use something new (very new, ground level, not all features out yet) called Amsel Suite, Google Docs, DND Beyond and Discord.

Twine: Twine / An open-source tool for telling interactive, nonlinear stories is really great for this. Two fellow DMs and I appreciate its ease of use, multi-chapter functionality, and the ability to link to anything on D&D Beyond.  Can't share with the party though.

If you're using an online VTT, like Roll20, you can make handouts for the party that they can then go back and look at when needed.