Personal Knowledge Management Systems (PKMS)

Obsidian + I have a system where everything is an object and each object is a .md note. No folders. Objects can link to other objects as their type (THE_MATRIX_1999 links MOVIE as its type for example), objects can also be linked like this (related to XYZ, prequel to XYZ) or anything else really. I can create infinite virtual hierarchies this way. I also have a system that randomly reminds me/features certain notes/objects, on da daily basis - so I never forget about a note I may care about forever. I can also adjust how often I want each object to be featured to me from daily all the way up to infinitely rarely.

I also use Obsidian, and I use Todoist. I use lots of daily notes when I want to jot things down. Facts and ideas go into basically a Zettelkasten system. I also keep a GTD-style directory structure for reference material - stuff like tax forms, info for kids' schools, etc. I make a lot of use of the Folder Note plugin for that.

For todos I use a GTD system with action priorities. So I have lots of projects which mostly have one or two actions each. I mix some ideas from GTD, and from one of my wife's favorite books, How to Get Control of Your Time and Your Life by Alan Lakein. I have a view that collects all actions in one place, but only shows actions that are prioritized, and aren't due yet, and aren't labeled as blocked.

For a while I used Obsidian for todos using the Dataview plugin to collect, sort, and filter todos. I used the Quickadd plugin to capture todos. What I liked about that system was it made reviews easy: I had a document with headings for each project with next actions for each. The reason I switched is that I wasn't looking at my next actions list often enough, and I didn't have a way to show notifications when something should be done at a specific time. Even when I thought about checking my todos, and I had a home screen shortcut to my next actions document, opening Obsidian on Android is slow enough to add friction. Todoist helps with a home screen widget, notifications, and by opening faster.