I'll skip the common ones that are frequently mentioned to give Zim some love! Zim is a desktop wiki app which, as implied, allows you to make your own private wiki which is invaluable for my writing and worldbuilding hobby.
i had switched after losing a D&D campaign in onenote, then not long after switched from windows to linux (Zim being compatible with both helped with that a lot too). I have a memory problem (in my carbon, not my silicon) and I use Zim for to do lists, a journal, note taking of course and several other things. i had some issues a few times but overall it's what just works for me. i use it for worldbuilding D&D campaigns and i've started building/recording my actual real life world with it too. love it!