TaskPocket is a to-do app that stays small. Inbox, Today, Upcoming, Someday, and projects grouped into areas. That's the whole system, so there's nothing to set up. Type "water the plants every other saturday at 10am" and you get the date, the repeat, and a reminder. Notes, checklists, tags, and files on every task, with previews right in the browser. Works in any browser, and the iPhone app works offline. The free plan has unlimited tasks.