What kind of integration between your todos and knowledge? If you haven't found one, how about building your own todo app that fits your needs. I have a demo here https://community.sitegui.com/blog/creating-the-first-applic...
Struggling with info all over the place as well I'm using AI to search for info in my notes at https://saner.ai/ Eating my own dog food here lol but it works Preparing to add todo list into the app as well
Any desktop or mobile app in your roadmap?
I use emacs org mode (and emacs org node and emacs org agenda), and Orgzly Revived on Android (the latter can do DAV sync). It's quite nice and can do integration, search and quick capture, TODOs. It's also endlessly customizable--but I almost don't customize it.
Zim - Wysiwyg for markdown files
My only complaints are that it uses .txt instead of .md and that I haven't been able to get it to work on Mac.
Most recently Obsidian with PARA method.
Obsidian isn't open source unfortunately, but I'd guess you could achieve a very similar setup with logseq.
I'm planning on migrating to org-roam though
Trello: I could care less about open source or self hostable. It’s a tool
There is a Mac, Windows, Web, iOS, and Android app. Simple Kanban board like interface and I can add comments and descriptions in markdown for each entry.
Obsidian sounds exactly like what you're looking for. It's not a todo app out of the box, but community extensions can easily adapt it to fit your needs.
Not FOSS, but check out Craft https://www.craft.do/
I'm using NotePlan (https://noteplan.co) and loving it.
It's a macOS/iOS app (there's a somewhat limited Web version). IMO, the best balance between PKM and task manager/calendar management.
I've also tried Amplenote (https://amplenote.com) that has some of the features you want but the tagging concept lost me.
I think there are some Workflowy clones that are OSS but I like the original.
Standard Notes.
Excel / Google Spreadsheets?