This is the system I use to manage my to-dos. It may seem complex, but most of the machinery works in the background, and the interface is mostly just text. I like how little is in the way of the doing — it really works for me.
I group similar tasks together in text files and edit them with FoldingText (which is designed for working with lists formatted in Markdown).
This isn’t revolutionary — these are just text files. But, that means it’s super easy to add, edit, and sort. And I can complete a task by deleting the line (⌘ + ⌥ + Delete), all using the keyboard.
The main file is Tasks.txt. But I have others — Journal.txt (thoughts for journaling), Buy.txt (grocery list), Links.txt (stuff to read and watch later), Friends.txt (notes for future conversations), and more.
I use LaunchBar to open lists when I need them. And since the files are stored locally, they open and save really quickly.
The files are synced to Dropbox, which allows for some cool automagic stuff. Any changes in the cloud are immediately visible on my Mac (even if the file’s open).
Apple Calendar → Google Calendar
I have a dedicated calendar for tasks. The scheduled date/time is when I want the task to appear on Tasks.txt — not the task’s due date. If there is a due date, I note it in the task name. As with any calendar event, these tasks can repeat, too (like watering the plants).
Apple and Google Calendars sync, which enables more automagic.
Google Calendar → IFTTT → Dropbox → Tasks.txt
When a task hits its scheduled date/time, it’s added to Tasks.txt automatically — using IFTTT to connect Google Calendar and Dropbox.
LaunchBar → Apple Calendar
With LaunchBar on my Mac, I can schedule tasks crazy quickly (using only the keyboard). Using LaunchBar means that the tasks calendar is a mostly invisible part of this system that just does its thing in the background.
To postpone a task, I just re-add it to the calendar with a new date.
Drafts → Dropbox → Tasks.txt
I tend to process thoughts better when I can get them out of my head and make room for more. I use Drafts on my iPhone for this instead of a paper notebook. It’s become an essential tool for the way I think, and I use it maybe more than any other iOS app (10–20 times a day).
I just type the task and send it to Tasks.txt (or any of my other lists).
Dropbox → 1Writer
FoldingText doesn’t have a mobile app, so I use 1Writer instead — especially useful for the grocery list.