I currently leverage Onenote as my go to home brewed database of information as it relates to my campaign.  I am in absolute high hopes that D&D Beyond will replace this approach.  Worst case, I will be linking URLs from D&D Beyond into my Onenote pages.

What are other DM's using to manage campaigns? Encounters? PC information? Etc?

I stick with the good old pen and paper with a 3 ring binder with everything separated. Bit harder to track, but I manage. That's why I can't wait for this haha.

Evernote and Google Docs. I hope to integrate this with those.

I've been using Google Drive for all my groups needs.  We use Tabletop Simulator, as we all live in different areas of the US, and gather on Discord for voice chat/dice rolling.

I DM and have each player share their Google Sheet with me, which I reference the link to in a 'Master' sheet.  Each player is a tab in my sheet, allowing me scroll through quickly to view stats/gear/etc.  I use Docs to write campaign events and dialog that NPCs will have at the ready, such as answers, questions, and whatnot.  Also, all images and maps are kept here as well.

I have become very comfortable with this layout - Beyond will need to impress to get me to uproot, as I will likely continue to have information needing to be kept externally from their software.

http://www.dndbeyond.com/forums/dungeons-dragons-discussion/homebrew-house-rules/402-a-list-of-qol-imoving-tools-for-5th-edition

This might be helpful. 

Yeah I'm using Cryrid's Onenote and I've mostly filled it out... This and that are basically the same thing.... That's offline and doesn't cost me anything at the moment though. So we'll see :) High hopes for this thing. Though I don't really like my players having super easy access to monsters right next to their character stats... promotoes meta gaming.

I'm a big proponent of the one note system as well. Although, I'd love some kind of player-facing customizable features for loading world maps, town maps, and destinations...especially if it melded with downtime/travel and other rules. A boy can dream...

I'm surprised this hasn't been mentioned already, but I use Roll20 for pretty much everything in my campaign. 

I use the game forums as a way to keep track of the goings on of the party. This lets the players keep a campaign diary (instead of me), which lets me know what they are thinking/feeling is going on in the world. I find that way is much better than ME recapping the adventure, because of course I know everything that's going on, but perhaps they missed a key piece of info, which this has the benefit of letting you know if they missed something that you assumed they knew. That way, you can drop hints about/clarify things that they might need to know (or not, if they don't NEED to know it). 

Like, maybe they don't need to know Random-Smith A's name is Bobo, but they will certainly need to know the name of the town that the wizard who gave them the quest told them to go to (but maybe they don't need to be reminded that the wizard covered up his notes on necromancy when they first entered the room). 

For sharing files, I just use Google Drive, because it's free and everyone already had an account.

I definitely use a lot of OneNote. I basically have the PHB/DMG/MM in there. Plus many many campaign notes. Love it.

I like the "the party keeps notes" bit. As it stands I only have one diligent note taker in the party but it would be nice to have all their notes and see how they interpreted events.

Roll20 is so useful and easy to keep track of stuff. I have used it for battle maps and showing the party the world map before, but now it's mainly used as a place for people to roll and keep track of their character sheets. And lots of immature doodles.

Google drive for my notes and Discord for the actual calls. Dropping in and out at will is wonderful. The folks that made Discord deserve a medal or something.

Pen & paper would do the best all the time. Using homebrew sheets to keep all infos in a one paper. As online, Fantasy Grounds do all the dirty work :)

I write insta notes to google docs, and keep them in the final shape at ObsidianPortal

Using both pen&paper and onenote.

I usually use Orcpub when it comes to combat to help track health and how many rounds have gone by, which is always something I forget. 

I use software designed specifically for DMs to manage this information. It's called Realm Works and it blows OneNote out of the water IMO. The one and only benefit OneNote has is it can be accessed via the web from any device. Which Realm Works is working on. You really have to see the tool in action to understand it's power. 

Realm Works and Hero Labs - A DM Tour

I also use OneNote for all my games. I'd say it's the best I've seen by far, combined with a Dropbox for files.

As someone who used to do corporate trainings on One Note, I'm a big proponent of it and use it for most of my other games (e.g. Star Wars RPG, Numenera, etc.) I don't use it for DnD however. (I use an a popular app, that shall remain nameless so as to not call attention to it should WotC get jealous, that I have expanded with XML databases.) One tool that I find helpful, especially for planning and writing adventures, is Scrivener. It has a lot of similar functionality to One Note but I find it easier to write for long periods of time within it. Otherwise, my groups use Google Drive and Dropbox to share files, character sheets, PDFs, and other materials.

For me Trello is the way to go.