Any recommendations?
https://www.zotero.org/ is not just a citation manager. I look at it as a DB of archived pages, pdfs, and bookmarks.
https://logseq.com/ is an "advanced" outliner. So for gathering thoughts, it is both highly hierarchical (= outlining) and non-linear (through tagging and links).
It is a powerful combo, so it could be overwhelming for simpler use cases.
It's not open-sourced yet (on our roadmap), but free in a large part, local-first (running on plain text .md files) and designed for quickly capturing stuff as well as accessing. Would love to get your feedback.