It's not an exaggeration to say that org-mode changed my life. I started using it after my first year as a freelancer; I was really struggling to get myself organized and was prepping myself to get out of software entirely.

Switching to org-mode helped me keep on top of everything in a way I'd never really experienced before. Since then I've expanded my usage of org considerably - I use it for taking notes, tracking my diet+exercise, and planning out my projects (more info here: https://www.philnewton.net/blog/emacs-org/).

It's not everybody's cup of tea, but for me it fits my mental models better than anything I've ever used.