I keep a wiki using obsidian.md. The hard work is in working up the motivation to keep it updated. API keys and such I like to keep in Bitwarden/Vaultwarden

Secrets in BitWarden, documentation in Bookstack.

Right now: Keepass and a note-taking app I’m hoping others will post far better options so that I can improve my organization…

I keep all secrets and passwords in a selfhosted Bitwarden instance. I don't maintain any kind of "documentation" since my deployment files and scripts are clean and tidy, so I can tell what's going on at a glance by looking at them directly. They're also constantly changing as I continuously harden services according to ever-changing standards, so it's more efficient for me to just continue keeping my codebase clean than it is to maintain separate documentation that I myself will likely never read again once I've published it.

I'm the only one that needs to know how my own services are deployed and what the infrastructure looks like, and it's way faster for me to just look at the actual content of whatever deployment files or scripts I have.

It's a different story for things I work with professionally, because you can't trust someone else working to maintain the same things as you has the same level of knowledge to "just know where to go and what to do". But that doesn't apply to personal projects where I just want to get things done.

As others have mentioned, there are two things required. A space to document information, and a separate secure space for password/secretes.

Personally I use Joplin and BitWarden. I used to use DokuWIki and KeepassXC.

Secrets in password manager, documentation in NixOS configuration files.

Keepassxc for passwords plus a big emacs .org notes file for documentation. The latter could be better organised but it's easy to search with emacs tools so it'll do.

KeePass, mainly.

Half of my passwords are stored with "password manager", which can be easily plugged to anything. For the rest, I use ansible to manage all my services and thus some secrets are also stored in an ansible vault file. The way my ansible playbooks are organized/commented serves as documentation.

Vaultwarden for secrets/passwords, Tiddlywiki for notes.

I keep all my secrets/passwords/keys in vaultwarden that replicates itself each night to an offsite VM. I also keep a mediawiki with how to's and the like. Network Diagram using draw.io

Edit: I also use Netbox to keep track of things such as device locations, serial numbers, cables, and IP addresses.