Planny.co - Planny is lightweight Twitter scheduler. Grow faster with calendar planner, multi account management, advanced drafts and analytics.
Later Reminders - Super simple way to schedule reminders on your phone
Day Night - A desktop app that kills the procrastination in you.
doo - A smart, simple app for reminders and to-dos
Gone - An ephemeral to-do list
Tiny Reminder - Collect content & files from busy clients