The ultimate open standards - pen and paper.

I find writing it down helps me remember the tasks or things needed, and a fountain pen is just a joy to use plus you get to take mini breaks from the digital world.

There are at least two very deep rabbit holes with fountain pens: inks, and vintage pens.

Writing with an ink the color of Crimson Glory Vine, for example, is a meditation all on its own (Pilot Iroshizuku Yama-Budo).

The vintage pens rabbit hole tends to force you toward inks that are "safe" for vintage pens (Waterman Serenity Blue, for example).

But either way, what you write with them, and what system you use is constrained only by imagination.