The best system I have, as someone with ADHD, is keeping a notebook with a handwritten todo list.
All I have to do in a week is make sure to finish the todos I write down.
That’s it.
I use the calendar for meetings and things I want my phone to remind me about, but most everything is in a handwritten todo list that I keep visible on my desk at all times.
I like handwritten notes too but it's hard to keep up with and still has the 'wall of awful' effect on me if there's something too tough in there.
You might like this little bookmarklet I built for quick notes in your browser when you can't be bothered to find/write in your notebook - I use it for quick work tasks a lot.
I use a daily diary notebook [1] with each page a todo for that day. First thing every day is reviewing the todo for that day, adding stuff that I didn't get done previously to today's or future day's todo. I try to be deliberate only adding stuff I intend to tackle today to today's list and putting the rest on future lists.
It seems to strike a balance between being flexible and letting me roll with things as they come at me, while also keeping my list of things to do at a manageable level so that I'm not distracted by stuff far in the future and not feeling like I'm not making any progress on things.
All I have to do in a week is make sure to finish the todos I write down.
That’s it.
I use the calendar for meetings and things I want my phone to remind me about, but most everything is in a handwritten todo list that I keep visible on my desk at all times.