Obsidian

Obsidian suits writers, researchers and people building a long-lived personal knowledge base. Notes remain files on your device, so you can organize ideas without committing everything to a hosted document format. Links and the graph are useful for tracing relationships across a growing collection.

The tradeoff is that you shape the system yourself. Plugins and themes offer flexibility, but a simple folder structure and a few useful conventions are a better starting point than installing every extension. Syncing devices and publishing notes are separate choices from the free editor.