Getting Things Done methodology
https://en.wikipedia.org/wiki/Getting_Things_Done
I've been practicing GTD in one fashion or other since around 2000 when Palm devices were all the rage, and the Internet bubble was but a mere sphere in everyone's eye. It's the one productivity system that stuck for me and it's what I try to practice on a daily basis.
It's not for everyone, but I've had good luck with it.