There are a lot of fancier note taking tools but I keep going back to Zim. Been using it for years for private offline note-taking for work. I use quick notes and journal shortcuts many times a day to quickly jot down a followup note/idea/question in meetings. It's also my GTD system with tasks plugin. Love that it's just text files so I can manually edit them, version control, sync in private cloud service, etc. Never worry about losing my data.
There are a few quirks I've gotten used to over the years though:
- Pasting code will be garbled or auto-create tags unless you use the source view plugin or paste verbatim.
- Takes a little configuration out of the box to get just right, system dependencies, links opening in right browser, plugins, shortcuts, fonts. But once you get streamlined it just works.
- The syntax feels a little strange to me but I rarely need to edit raw files. I could also export to Markdown if I ever wanted to migrate.
My last tip, templates are awesome. I have ones for all kinds of things, like interviewing, 1-1s, and architecture design outline.