Obsidian
Obsidian is a powerful note-taking tool that helps you organise and connect your thoughts. It uses Markdown for formatting and allows you to create a network of interconnected notes. Obsidian follows a file over app philosophy: the app may not be open source, but users have full control and access to their notes in the form of simple text/markdown files.
Pros:
- No lock-in: notes are saved as raw markdown files
- Lots of plugins available
Cons:
- Multi-device / collaboration requires a subscription or workarounds (e.g. Syncthing)
- As an Electron-based app, it requires a chunky bit of RAM (300MB+)