LaTeX Templates
I use LaTex for a lot of my note taking (for typesetting all equations certainly). When I first started using it, I remember the absolute horror of trying to get it to work with BibTex. The learning curve is relatively steep for non-programmers (I learnt it basically in parallel with learning to code) but it's certainly one of the most valuable tools I've learned and one I continually come back to for a huge range of projects. Certainly in an academic environment it continues to surprise me that everyone isn't taught LaTex in their first year of a PhD.