I'm old school, so I just constantly email myself replies to my past email with a reply to a past email with a past email with a todo list that I freshly created after finally crossing off the old ones.

It helps me sleep to add stuff to my todo list so I can offload anxiety about remembering said thing. It's great, I stole it a bit from a Buddhist meditation practice, but found I didn't trust promises I made to myself that if something is important I'll remember it later. Too much important stuff is planning and I don't like needing to burden others with reminding me to do things.